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<title>The GNU C Library: 1. Introduction</title>
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<td valign="middle" align="left">[<a href="libc_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
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<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top"><a href="libc_1.html#Introduction">1. Introduction</a></td><td> </td><td align="left" valign="top"> Purpose of the GNU C Library.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_2.html#Error-Reporting">2. Error Reporting</a></td><td> </td><td align="left" valign="top"> How library functions report errors.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Memory">3. Virtual Memory Allocation And Paging</a></td><td> </td><td align="left" valign="top"> Allocating virtual memory and controlling
paging.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_4.html#Character-Handling">4. Character Handling</a></td><td> </td><td align="left" valign="top"> Character testing and conversion functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#String-and-Array-Utilities">5. String and Array Utilities</a></td><td> </td><td align="left" valign="top"> Utilities for copying and comparing strings
and arrays.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Character-Set-Handling">6. Character Set Handling</a></td><td> </td><td align="left" valign="top"> Support for extended character sets.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Locales">7. Locales and Internationalization</a></td><td> </td><td align="left" valign="top"> The country and language can affect the
behavior of library functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#Message-Translation">8. Message Translation</a></td><td> </td><td align="left" valign="top"> How to make the program speak the user’s
language.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_9.html#Searching-and-Sorting">9. Searching and Sorting</a></td><td> </td><td align="left" valign="top"> General searching and sorting functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Pattern-Matching">10. Pattern Matching</a></td><td> </td><td align="left" valign="top"> Matching shell “globs” and regular
expressions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_11.html#I_002fO-Overview">11. Input/Output Overview</a></td><td> </td><td align="left" valign="top"> Introduction to the I/O facilities.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#I_002fO-on-Streams">12. Input/Output on Streams</a></td><td> </td><td align="left" valign="top"> High-level, portable I/O facilities.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_13.html#Low_002dLevel-I_002fO">13. Low-Level Input/Output</a></td><td> </td><td align="left" valign="top"> Low-level, less portable I/O.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_14.html#File-System-Interface">14. File System Interface</a></td><td> </td><td align="left" valign="top"> Functions for manipulating files.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_15.html#Pipes-and-FIFOs">15. Pipes and FIFOs</a></td><td> </td><td align="left" valign="top"> A simple interprocess communication
mechanism.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_16.html#Sockets">16. Sockets</a></td><td> </td><td align="left" valign="top"> A more complicated IPC mechanism, with
networking support.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_17.html#Low_002dLevel-Terminal-Interface">17. Low-Level Terminal Interface</a></td><td> </td><td align="left" valign="top"> How to change the characteristics of a
terminal device.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_18.html#Syslog">18. Syslog</a></td><td> </td><td align="left" valign="top"> System logging and messaging.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_19.html#Mathematics">19. Mathematics</a></td><td> </td><td align="left" valign="top"> Math functions, useful constants, random
numbers.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_20.html#Arithmetic">20. Arithmetic Functions</a></td><td> </td><td align="left" valign="top"> Low level arithmetic functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_21.html#Date-and-Time">21. Date and Time</a></td><td> </td><td align="left" valign="top"> Functions for getting the date and time and
formatting them nicely.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_22.html#Resource-Usage-And-Limitation">22. Resource Usage And Limitation</a></td><td> </td><td align="left" valign="top"> Functions for examining resource usage and
getting and setting limits.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_23.html#Non_002dLocal-Exits">23. Non-Local Exits</a></td><td> </td><td align="left" valign="top"> Jumping out of nested function calls.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_24.html#Signal-Handling">24. Signal Handling</a></td><td> </td><td align="left" valign="top"> How to send, block, and handle signals.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_25.html#Program-Basics">25. The Basic Program/System Interface</a></td><td> </td><td align="left" valign="top"> Writing the beginning and end of your
program.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_26.html#Processes">26. Processes</a></td><td> </td><td align="left" valign="top"> How to create processes and run other
programs.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_27.html#Job-Control">27. Job Control</a></td><td> </td><td align="left" valign="top"> All about process groups and sessions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_28.html#Name-Service-Switch">28. System Databases and Name Service Switch</a></td><td> </td><td align="left" valign="top"> Accessing system databases.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_29.html#Users-and-Groups">29. Users and Groups</a></td><td> </td><td align="left" valign="top"> How users are identified and classified.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_30.html#System-Management">30. System Management</a></td><td> </td><td align="left" valign="top"> Controlling the system and getting
information about it.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_31.html#System-Configuration">31. System Configuration Parameters</a></td><td> </td><td align="left" valign="top"> Parameters describing operating system
limits.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_32.html#Cryptographic-Functions">32. DES Encryption and Password Handling</a></td><td> </td><td align="left" valign="top"> DES encryption and password handling.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_33.html#Debugging-Support">33. Debugging support</a></td><td> </td><td align="left" valign="top"> Functions to help debugging applications.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Appendices
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_34.html#Language-Features">A. C Language Facilities in the Library</a></td><td> </td><td align="left" valign="top"> C language features provided by the library.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_35.html#Library-Summary">B. Summary of Library Facilities</a></td><td> </td><td align="left" valign="top"> A summary showing the syntax, header file,
and derivation of each library feature.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_36.html#Installation">C. Installing the GNU C Library</a></td><td> </td><td align="left" valign="top"> How to install the GNU C library.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_37.html#Maintenance">D. Library Maintenance</a></td><td> </td><td align="left" valign="top"> How to enhance and port the GNU C Library.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_38.html#Contributors">E. Contributors to the GNU C Library</a></td><td> </td><td align="left" valign="top"> Who wrote what parts of the GNU C library.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_39.html#Free-Manuals">F. Free Software Needs Free Documentation</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_40.html#Copying">G. GNU Lesser General Public License</a></td><td> </td><td align="left" valign="top"> The GNU Lesser General Public License says
how you can copy and share the GNU C Library.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_41.html#Documentation-License">H. GNU Free Documentation License</a></td><td> </td><td align="left" valign="top"> This manual is under the GNU Free
Documentation License.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Indices
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_42.html#Concept-Index">Concept Index</a></td><td> </td><td align="left" valign="top"> Index of concepts and names.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_50.html#Type-Index">Type Index</a></td><td> </td><td align="left" valign="top"> Index of types and type qualifiers.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_52.html#Function-Index">Function and Macro Index</a></td><td> </td><td align="left" valign="top"> Index of functions and function-like macros.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_61.html#Variable-Index">Variable and Constant Macro Index</a></td><td> </td><td align="left" valign="top"> Index of variables and variable-like macros.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_70.html#File-Index">Program and File Index</a></td><td> </td><td align="left" valign="top"> Index of programs and files.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
— The Detailed Node Listing —
Introduction
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_1.html#Getting-Started">1.1 Getting Started</a></td><td> </td><td align="left" valign="top"> What this manual is for and how to use it.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#Standards-and-Portability">1.2 Standards and Portability</a></td><td> </td><td align="left" valign="top"> Standards and sources upon which the GNU
C library is based.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#Using-the-Library">1.3 Using the Library</a></td><td> </td><td align="left" valign="top"> Some practical uses for the library.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#Roadmap-to-the-Manual">1.4 Roadmap to the Manual</a></td><td> </td><td align="left" valign="top"> Overview of the remaining chapters in
this manual.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Standards and Portability
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_1.html#ISO-C">1.2.1 ISO C</a></td><td> </td><td align="left" valign="top"> The international standard for the C
programming language.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#POSIX">1.2.2 POSIX (The Portable Operating System Interface)</a></td><td> </td><td align="left" valign="top"> The ISO/IEC 9945 (aka IEEE 1003) standards
for operating systems.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#Berkeley-Unix">1.2.3 Berkeley Unix</a></td><td> </td><td align="left" valign="top"> BSD and SunOS.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#SVID">1.2.4 SVID (The System V Interface Description)</a></td><td> </td><td align="left" valign="top"> The System V Interface Description.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#XPG">1.2.5 XPG (The X/Open Portability Guide)</a></td><td> </td><td align="left" valign="top"> The X/Open Portability Guide.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Using the Library
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_1.html#Header-Files">1.3.1 Header Files</a></td><td> </td><td align="left" valign="top"> How to include the header files in your
programs.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#Macro-Definitions">1.3.2 Macro Definitions of Functions</a></td><td> </td><td align="left" valign="top"> Some functions in the library may really
be implemented as macros.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#Reserved-Names">1.3.3 Reserved Names</a></td><td> </td><td align="left" valign="top"> The C standard reserves some names for
the library, and some for users.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_1.html#Feature-Test-Macros">1.3.4 Feature Test Macros</a></td><td> </td><td align="left" valign="top"> How to control what names are defined.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Error Reporting
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_2.html#Checking-for-Errors">2.1 Checking for Errors</a></td><td> </td><td align="left" valign="top"> How errors are reported by library functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_2.html#Error-Codes">2.2 Error Codes</a></td><td> </td><td align="left" valign="top"> Error code macros; all of these expand
into integer constant values.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_2.html#Error-Messages">2.3 Error Messages</a></td><td> </td><td align="left" valign="top"> Mapping error codes onto error messages.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Memory
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_3.html#Memory-Concepts">3.1 Process Memory Concepts</a></td><td> </td><td align="left" valign="top"> An introduction to concepts and terminology.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Memory-Allocation">3.2 Allocating Storage For Program Data</a></td><td> </td><td align="left" valign="top"> Allocating storage for your program data
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Locking-Pages">3.4 Locking Pages</a></td><td> </td><td align="left" valign="top"> Preventing page faults
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Resizing-the-Data-Segment">3.3 Resizing the Data Segment</a></td><td> </td><td align="left" valign="top"> <code>brk</code>, <code>sbrk</code>
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Memory Allocation
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_3.html#Memory-Allocation-and-C">3.2.1 Memory Allocation in C Programs</a></td><td> </td><td align="left" valign="top"> How to get different kinds of allocation in C.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Unconstrained-Allocation">3.2.2 Unconstrained Allocation</a></td><td> </td><td align="left" valign="top"> The <code>malloc</code> facility allows fully general
dynamic allocation.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Allocation-Debugging">3.2.3 Allocation Debugging</a></td><td> </td><td align="left" valign="top"> Finding memory leaks and not freed memory.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Obstacks">3.2.4 Obstacks</a></td><td> </td><td align="left" valign="top"> Obstacks are less general than malloc
but more efficient and convenient.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Variable-Size-Automatic">3.2.5 Automatic Storage with Variable Size</a></td><td> </td><td align="left" valign="top"> Allocation of variable-sized blocks
of automatic storage that are freed when the
calling function returns.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Unconstrained Allocation
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_3.html#Basic-Allocation">3.2.2.1 Basic Memory Allocation</a></td><td> </td><td align="left" valign="top"> Simple use of <code>malloc</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Malloc-Examples">3.2.2.2 Examples of <code>malloc</code></a></td><td> </td><td align="left" valign="top"> Examples of <code>malloc</code>. <code>xmalloc</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Freeing-after-Malloc">3.2.2.3 Freeing Memory Allocated with <code>malloc</code></a></td><td> </td><td align="left" valign="top"> Use <code>free</code> to free a block you
got with <code>malloc</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Changing-Block-Size">3.2.2.4 Changing the Size of a Block</a></td><td> </td><td align="left" valign="top"> Use <code>realloc</code> to make a block
bigger or smaller.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Allocating-Cleared-Space">3.2.2.5 Allocating Cleared Space</a></td><td> </td><td align="left" valign="top"> Use <code>calloc</code> to allocate a
block and clear it.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Efficiency-and-Malloc">3.2.2.6 Efficiency Considerations for <code>malloc</code></a></td><td> </td><td align="left" valign="top"> Efficiency considerations in use of
these functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Aligned-Memory-Blocks">3.2.2.7 Allocating Aligned Memory Blocks</a></td><td> </td><td align="left" valign="top"> Allocating specially aligned memory.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Malloc-Tunable-Parameters">3.2.2.8 Malloc Tunable Parameters</a></td><td> </td><td align="left" valign="top"> Use <code>mallopt</code> to adjust allocation
parameters.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Heap-Consistency-Checking">3.2.2.9 Heap Consistency Checking</a></td><td> </td><td align="left" valign="top"> Automatic checking for errors.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Hooks-for-Malloc">3.2.2.10 Memory Allocation Hooks</a></td><td> </td><td align="left" valign="top"> You can use these hooks for debugging
programs that use <code>malloc</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Statistics-of-Malloc">3.2.2.11 Statistics for Memory Allocation with <code>malloc</code></a></td><td> </td><td align="left" valign="top"> Getting information about how much
memory your program is using.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Summary-of-Malloc">3.2.2.12 Summary of <code>malloc</code>-Related Functions</a></td><td> </td><td align="left" valign="top"> Summary of <code>malloc</code> and related functions.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Allocation Debugging
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_3.html#Tracing-malloc">3.2.3.1 How to install the tracing functionality</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Using-the-Memory-Debugger">3.2.3.2 Example program excerpts</a></td><td> </td><td align="left" valign="top"> Example programs excerpts.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Tips-for-the-Memory-Debugger">3.2.3.3 Some more or less clever ideas</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Interpreting-the-traces">3.2.3.4 Interpreting the traces</a></td><td> </td><td align="left" valign="top"> What do all these lines mean?
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Obstacks
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_3.html#Creating-Obstacks">3.2.4.1 Creating Obstacks</a></td><td> </td><td align="left" valign="top"> How to declare an obstack in your program.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Preparing-for-Obstacks">3.2.4.2 Preparing for Using Obstacks</a></td><td> </td><td align="left" valign="top"> Preparations needed before you can
use obstacks.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Allocation-in-an-Obstack">3.2.4.3 Allocation in an Obstack</a></td><td> </td><td align="left" valign="top"> Allocating objects in an obstack.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Freeing-Obstack-Objects">3.2.4.4 Freeing Objects in an Obstack</a></td><td> </td><td align="left" valign="top"> Freeing objects in an obstack.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Obstack-Functions">3.2.4.5 Obstack Functions and Macros</a></td><td> </td><td align="left" valign="top"> The obstack functions are both
functions and macros.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Growing-Objects">3.2.4.6 Growing Objects</a></td><td> </td><td align="left" valign="top"> Making an object bigger by stages.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Extra-Fast-Growing">3.2.4.7 Extra Fast Growing Objects</a></td><td> </td><td align="left" valign="top"> Extra-high-efficiency (though more
complicated) growing objects.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Status-of-an-Obstack">3.2.4.8 Status of an Obstack</a></td><td> </td><td align="left" valign="top"> Inquiries about the status of an obstack.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Obstacks-Data-Alignment">3.2.4.9 Alignment of Data in Obstacks</a></td><td> </td><td align="left" valign="top"> Controlling alignment of objects in obstacks.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Obstack-Chunks">3.2.4.10 Obstack Chunks</a></td><td> </td><td align="left" valign="top"> How obstacks obtain and release chunks;
efficiency considerations.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Summary-of-Obstacks">3.2.4.11 Summary of Obstack Functions</a></td><td> </td><td align="left" valign="top">
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Variable Size Automatic
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_3.html#Alloca-Example">3.2.5.1 <code>alloca</code> Example</a></td><td> </td><td align="left" valign="top"> Example of using <code>alloca</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Advantages-of-Alloca">3.2.5.2 Advantages of <code>alloca</code></a></td><td> </td><td align="left" valign="top"> Reasons to use <code>alloca</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Disadvantages-of-Alloca">3.2.5.3 Disadvantages of <code>alloca</code></a></td><td> </td><td align="left" valign="top"> Reasons to avoid <code>alloca</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#GNU-C-Variable_002dSize-Arrays">3.2.5.4 GNU C Variable-Size Arrays</a></td><td> </td><td align="left" valign="top"> Only in GNU C, here is an alternative
method of allocating dynamically and
freeing automatically.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Locking Pages
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_3.html#Why-Lock-Pages">3.4.1 Why Lock Pages</a></td><td> </td><td align="left" valign="top"> Reasons to read this section.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Locked-Memory-Details">3.4.2 Locked Memory Details</a></td><td> </td><td align="left" valign="top"> Everything you need to know locked
memory
</td></tr>
<tr><td align="left" valign="top"><a href="libc_3.html#Page-Lock-Functions">3.4.3 Functions To Lock And Unlock Pages</a></td><td> </td><td align="left" valign="top"> Here’s how to do it.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Character Handling
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_4.html#Classification-of-Characters">4.1 Classification of Characters</a></td><td> </td><td align="left" valign="top"> Testing whether characters are
letters, digits, punctuation, etc.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_4.html#Case-Conversion">4.2 Case Conversion</a></td><td> </td><td align="left" valign="top"> Case mapping, and the like.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_4.html#Classification-of-Wide-Characters">4.3 Character class determination for wide characters</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_4.html#Using-Wide-Char-Classes">4.4 Notes on using the wide character classes</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_4.html#Wide-Character-Case-Conversion">4.5 Mapping of wide characters.</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
String and Array Utilities
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_5.html#Representation-of-Strings">5.1 Representation of Strings</a></td><td> </td><td align="left" valign="top"> Introduction to basic concepts.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#String_002fArray-Conventions">5.2 String and Array Conventions</a></td><td> </td><td align="left" valign="top"> Whether to use a string function or an
arbitrary array function.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#String-Length">5.3 String Length</a></td><td> </td><td align="left" valign="top"> Determining the length of a string.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Copying-and-Concatenation">5.4 Copying and Concatenation</a></td><td> </td><td align="left" valign="top"> Functions to copy the contents of strings
and arrays.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#String_002fArray-Comparison">5.5 String/Array Comparison</a></td><td> </td><td align="left" valign="top"> Functions for byte-wise and character-wise
comparison.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Collation-Functions">5.6 Collation Functions</a></td><td> </td><td align="left" valign="top"> Functions for collating strings.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Search-Functions">5.7 Search Functions</a></td><td> </td><td align="left" valign="top"> Searching for a specific element or substring.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Finding-Tokens-in-a-String">5.8 Finding Tokens in a String</a></td><td> </td><td align="left" valign="top"> Splitting a string into tokens by looking
for delimiters.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#strfry">5.9 strfry</a></td><td> </td><td align="left" valign="top"> Function for flash-cooking a string.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Trivial-Encryption">5.10 Trivial Encryption</a></td><td> </td><td align="left" valign="top"> Obscuring data.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Encode-Binary-Data">5.11 Encode Binary Data</a></td><td> </td><td align="left" valign="top"> Encoding and Decoding of Binary Data.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Argz-and-Envz-Vectors">5.12 Argz and Envz Vectors</a></td><td> </td><td align="left" valign="top"> Null-separated string vectors.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Argz and Envz Vectors
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_5.html#Argz-Functions">5.12.1 Argz Functions</a></td><td> </td><td align="left" valign="top"> Operations on argz vectors.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_5.html#Envz-Functions">5.12.2 Envz Functions</a></td><td> </td><td align="left" valign="top"> Additional operations on environment vectors.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Character Set Handling
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_6.html#Extended-Char-Intro">6.1 Introduction to Extended Characters</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Charset-Function-Overview">6.2 Overview about Character Handling Functions</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Restartable-multibyte-conversion">6.3 Restartable Multibyte Conversion Functions</a></td><td> </td><td align="left" valign="top"> Restartable multibyte conversion
Functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Non_002dreentrant-Conversion">6.4 Non-reentrant Conversion Function</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Generic-Charset-Conversion">6.5 Generic Charset Conversion</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Restartable multibyte conversion
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_6.html#Selecting-the-Conversion">6.3.1 Selecting the conversion and its properties</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Keeping-the-state">6.3.2 Representing the state of the conversion</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Converting-a-Character">6.3.3 Converting Single Characters</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Converting-Strings">6.3.4 Converting Multibyte and Wide Character Strings</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Multibyte-Conversion-Example">6.3.5 A Complete Multibyte Conversion Example</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Non-reentrant Conversion
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_6.html#Non_002dreentrant-Character-Conversion">6.4.1 Non-reentrant Conversion of Single Characters</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Non_002dreentrant-String-Conversion">6.4.2 Non-reentrant Conversion of Strings</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Shift-State">6.4.3 States in Non-reentrant Functions</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Generic Charset Conversion
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_6.html#Generic-Conversion-Interface">6.5.1 Generic Character Set Conversion Interface</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#iconv-Examples">6.5.2 A complete <code>iconv</code> example</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#Other-iconv-Implementations">6.5.3 Some Details about other <code>iconv</code> Implementations</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_6.html#glibc-iconv-Implementation">6.5.4 The <code>iconv</code> Implementation in the GNU C library</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Locales
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_7.html#Effects-of-Locale">7.1 What Effects a Locale Has</a></td><td> </td><td align="left" valign="top"> Actions affected by the choice of
locale.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Choosing-Locale">7.2 Choosing a Locale</a></td><td> </td><td align="left" valign="top"> How the user specifies a locale.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Locale-Categories">7.3 Categories of Activities that Locales Affect</a></td><td> </td><td align="left" valign="top"> Different purposes for which you can
select a locale.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Setting-the-Locale">7.4 How Programs Set the Locale</a></td><td> </td><td align="left" valign="top"> How a program specifies the locale
with library functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Standard-Locales">7.5 Standard Locales</a></td><td> </td><td align="left" valign="top"> Locale names available on all systems.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Locale-Information">7.6 Accessing Locale Information</a></td><td> </td><td align="left" valign="top"> How to access the information for the locale.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Formatting-Numbers">7.7 A dedicated function to format numbers</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Yes_002dor_002dNo-Questions">7.8 Yes-or-No Questions</a></td><td> </td><td align="left" valign="top"> Check a Response against the locale.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Locale Information
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_7.html#The-Lame-Way-to-Locale-Data">7.6.1 <code>localeconv</code>: It is portable but …</a></td><td> </td><td align="left" valign="top"> ISO C’s <code>localeconv</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#The-Elegant-and-Fast-Way">7.6.2 Pinpoint Access to Locale Data</a></td><td> </td><td align="left" valign="top"> X/Open’s <code>nl_langinfo</code>.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
The Lame Way to Locale Data
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_7.html#General-Numeric">7.6.1.1 Generic Numeric Formatting Parameters</a></td><td> </td><td align="left" valign="top"> Parameters for formatting numbers and
currency amounts.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Currency-Symbol">7.6.1.2 Printing the Currency Symbol</a></td><td> </td><td align="left" valign="top"> How to print the symbol that identifies an
amount of money (e.g. ‘<samp>$</samp>’).
</td></tr>
<tr><td align="left" valign="top"><a href="libc_7.html#Sign-of-Money-Amount">7.6.1.3 Printing the Sign of a Monetary Amount</a></td><td> </td><td align="left" valign="top"> How to print the (positive or negative) sign
for a monetary amount, if one exists.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Message Translation
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_8.html#Message-catalogs-a-la-X_002fOpen">8.1 X/Open Message Catalog Handling</a></td><td> </td><td align="left" valign="top"> The <code>catgets</code> family of functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#The-Uniforum-approach">8.2 The Uniforum approach to Message Translation</a></td><td> </td><td align="left" valign="top"> The <code>gettext</code> family of functions.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Message catalogs a la X/Open
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_8.html#The-catgets-Functions">8.1.1 The <code>catgets</code> function family</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#The-message-catalog-files">8.1.2 Format of the message catalog files</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#The-gencat-program">8.1.3 Generate Message Catalogs files</a></td><td> </td><td align="left" valign="top"> How to generate message catalogs files which
can be used by the functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#Common-Usage">8.1.4 How to use the <code>catgets</code> interface</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
The Uniforum approach
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_8.html#Message-catalogs-with-gettext">8.2.1 The <code>gettext</code> family of functions</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#Helper-programs-for-gettext">8.2.2 Programs to handle message catalogs for <code>gettext</code></a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Message catalogs with gettext
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_8.html#Translation-with-gettext">8.2.1.1 What has to be done to translate a message?</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#Locating-gettext-catalog">8.2.1.2 How to determine which catalog to be used</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#Advanced-gettext-functions">8.2.1.3 Additional functions for more complicated situations</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#Charset-conversion-in-gettext">8.2.1.4 How to specify the output character set <code>gettext</code> uses</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#GUI-program-problems">8.2.1.5 How to use <code>gettext</code> in GUI programs</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_8.html#Using-gettextized-software">8.2.1.6 User influence on <code>gettext</code></a></td><td> </td><td align="left" valign="top"> The possibilities of the user to influence
the way <code>gettext</code> works.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Searching and Sorting
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_9.html#Comparison-Functions">9.1 Defining the Comparison Function</a></td><td> </td><td align="left" valign="top"> Defining how to compare two objects.
Since the sort and search facilities
are general, you have to specify the
ordering.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_9.html#Array-Search-Function">9.2 Array Search Function</a></td><td> </td><td align="left" valign="top"> The <code>bsearch</code> function.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_9.html#Array-Sort-Function">9.3 Array Sort Function</a></td><td> </td><td align="left" valign="top"> The <code>qsort</code> function.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_9.html#Search_002fSort-Example">9.4 Searching and Sorting Example</a></td><td> </td><td align="left" valign="top"> An example program.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_9.html#Hash-Search-Function">9.5 The <code>hsearch</code> function.</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><td align="left" valign="top"><a href="libc_9.html#Tree-Search-Function">9.6 The <code>tsearch</code> function.</a></td><td> </td><td align="left" valign="top"></td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Pattern Matching
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_10.html#Wildcard-Matching">10.1 Wildcard Matching</a></td><td> </td><td align="left" valign="top"> Matching a wildcard pattern against a single string.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Globbing">10.2 Globbing</a></td><td> </td><td align="left" valign="top"> Finding the files that match a wildcard pattern.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Regular-Expressions">10.3 Regular Expression Matching</a></td><td> </td><td align="left" valign="top"> Matching regular expressions against strings.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Word-Expansion">10.4 Shell-Style Word Expansion</a></td><td> </td><td align="left" valign="top"> Expanding shell variables, nested commands,
arithmetic, and wildcards.
This is what the shell does with shell commands.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Globbing
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_10.html#Calling-Glob">10.2.1 Calling <code>glob</code></a></td><td> </td><td align="left" valign="top"> Basic use of <code>glob</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Flags-for-Globbing">10.2.2 Flags for Globbing</a></td><td> </td><td align="left" valign="top"> Flags that enable various options in <code>glob</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#More-Flags-for-Globbing">10.2.3 More Flags for Globbing</a></td><td> </td><td align="left" valign="top"> GNU specific extensions to <code>glob</code>.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Regular Expressions
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_10.html#POSIX-Regexp-Compilation">10.3.1 POSIX Regular Expression Compilation</a></td><td> </td><td align="left" valign="top"> Using <code>regcomp</code> to prepare to match.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Flags-for-POSIX-Regexps">10.3.2 Flags for POSIX Regular Expressions</a></td><td> </td><td align="left" valign="top"> Syntax variations for <code>regcomp</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Matching-POSIX-Regexps">10.3.3 Matching a Compiled POSIX Regular Expression</a></td><td> </td><td align="left" valign="top"> Using <code>regexec</code> to match the compiled
pattern that you get from <code>regcomp</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Regexp-Subexpressions">10.3.4 Match Results with Subexpressions</a></td><td> </td><td align="left" valign="top"> Finding which parts of the string were matched.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Subexpression-Complications">10.3.5 Complications in Subexpression Matching</a></td><td> </td><td align="left" valign="top"> Find points of which parts were matched.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Regexp-Cleanup">10.3.6 POSIX Regexp Matching Cleanup</a></td><td> </td><td align="left" valign="top"> Freeing storage; reporting errors.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Word Expansion
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_10.html#Expansion-Stages">10.4.1 The Stages of Word Expansion</a></td><td> </td><td align="left" valign="top"> What word expansion does to a string.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Calling-Wordexp">10.4.2 Calling <code>wordexp</code></a></td><td> </td><td align="left" valign="top"> How to call <code>wordexp</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Flags-for-Wordexp">10.4.3 Flags for Word Expansion</a></td><td> </td><td align="left" valign="top"> Options you can enable in <code>wordexp</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Wordexp-Example">10.4.4 <code>wordexp</code> Example</a></td><td> </td><td align="left" valign="top"> A sample program that does word expansion.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Tilde-Expansion">10.4.5 Details of Tilde Expansion</a></td><td> </td><td align="left" valign="top"> Details of how tilde expansion works.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_10.html#Variable-Substitution">10.4.6 Details of Variable Substitution</a></td><td> </td><td align="left" valign="top"> Different types of variable substitution.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
I/O Overview
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_11.html#I_002fO-Concepts">11.1 Input/Output Concepts</a></td><td> </td><td align="left" valign="top"> Some basic information and terminology.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_11.html#File-Names">11.2 File Names</a></td><td> </td><td align="left" valign="top"> How to refer to a file.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
I/O Concepts
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_11.html#Streams-and-File-Descriptors">11.1.1 Streams and File Descriptors</a></td><td> </td><td align="left" valign="top"> The GNU Library provides two ways
to access the contents of files.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_11.html#File-Position">11.1.2 File Position</a></td><td> </td><td align="left" valign="top"> The number of bytes from the
beginning of the file.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
File Names
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_11.html#Directories">11.2.1 Directories</a></td><td> </td><td align="left" valign="top"> Directories contain entries for files.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_11.html#File-Name-Resolution">11.2.2 File Name Resolution</a></td><td> </td><td align="left" valign="top"> A file name specifies how to look up a file.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_11.html#File-Name-Errors">11.2.3 File Name Errors</a></td><td> </td><td align="left" valign="top"> Error conditions relating to file names.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_11.html#File-Name-Portability">11.2.4 Portability of File Names</a></td><td> </td><td align="left" valign="top"> File name portability and syntax issues.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
I/O on Streams
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#Streams">12.1 Streams</a></td><td> </td><td align="left" valign="top"> About the data type representing a stream.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Standard-Streams">12.2 Standard Streams</a></td><td> </td><td align="left" valign="top"> Streams to the standard input and output
devices are created for you.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Opening-Streams">12.3 Opening Streams</a></td><td> </td><td align="left" valign="top"> How to create a stream to talk to a file.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Closing-Streams">12.4 Closing Streams</a></td><td> </td><td align="left" valign="top"> Close a stream when you are finished with it.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Streams-and-Threads">12.5 Streams and Threads</a></td><td> </td><td align="left" valign="top"> Issues with streams in threaded programs.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Streams-and-I18N">12.6 Streams in Internationalized Applications</a></td><td> </td><td align="left" valign="top"> Streams in internationalized applications.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Simple-Output">12.7 Simple Output by Characters or Lines</a></td><td> </td><td align="left" valign="top"> Unformatted output by characters and lines.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Character-Input">12.8 Character Input</a></td><td> </td><td align="left" valign="top"> Unformatted input by characters and words.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Line-Input">12.9 Line-Oriented Input</a></td><td> </td><td align="left" valign="top"> Reading a line or a record from a stream.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Unreading">12.10 Unreading</a></td><td> </td><td align="left" valign="top"> Peeking ahead/pushing back input just read.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Block-Input_002fOutput">12.11 Block Input/Output</a></td><td> </td><td align="left" valign="top"> Input and output operations on blocks of data.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Formatted-Output">12.12 Formatted Output</a></td><td> </td><td align="left" valign="top"> <code>printf</code> and related functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Customizing-Printf">12.13 Customizing <code>printf</code></a></td><td> </td><td align="left" valign="top"> You can define new conversion specifiers for
<code>printf</code> and friends.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Formatted-Input">12.14 Formatted Input</a></td><td> </td><td align="left" valign="top"> <code>scanf</code> and related functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#EOF-and-Errors">12.15 End-Of-File and Errors</a></td><td> </td><td align="left" valign="top"> How you can tell if an I/O error happens.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Error-Recovery">12.16 Recovering from errors</a></td><td> </td><td align="left" valign="top"> What you can do about errors.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Binary-Streams">12.17 Text and Binary Streams</a></td><td> </td><td align="left" valign="top"> Some systems distinguish between text files
and binary files.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#File-Positioning">12.18 File Positioning</a></td><td> </td><td align="left" valign="top"> About random-access streams.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Portable-Positioning">12.19 Portable File-Position Functions</a></td><td> </td><td align="left" valign="top"> Random access on peculiar ISO C systems.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Stream-Buffering">12.20 Stream Buffering</a></td><td> </td><td align="left" valign="top"> How to control buffering of streams.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Other-Kinds-of-Streams">12.21 Other Kinds of Streams</a></td><td> </td><td align="left" valign="top"> Streams that do not necessarily correspond
to an open file.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Formatted-Messages">12.22 Formatted Messages</a></td><td> </td><td align="left" valign="top"> Print strictly formatted messages.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Unreading
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#Unreading-Idea">12.10.1 What Unreading Means</a></td><td> </td><td align="left" valign="top"> An explanation of unreading with pictures.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#How-Unread">12.10.2 Using <code>ungetc</code> To Do Unreading</a></td><td> </td><td align="left" valign="top"> How to call <code>ungetc</code> to do unreading.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Formatted Output
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#Formatted-Output-Basics">12.12.1 Formatted Output Basics</a></td><td> </td><td align="left" valign="top"> Some examples to get you started.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Output-Conversion-Syntax">12.12.2 Output Conversion Syntax</a></td><td> </td><td align="left" valign="top"> General syntax of conversion
specifications.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Table-of-Output-Conversions">12.12.3 Table of Output Conversions</a></td><td> </td><td align="left" valign="top"> Summary of output conversions and
what they do.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Integer-Conversions">12.12.4 Integer Conversions</a></td><td> </td><td align="left" valign="top"> Details about formatting of integers.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Floating_002dPoint-Conversions">12.12.5 Floating-Point Conversions</a></td><td> </td><td align="left" valign="top"> Details about formatting of
floating-point numbers.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Other-Output-Conversions">12.12.6 Other Output Conversions</a></td><td> </td><td align="left" valign="top"> Details about formatting of strings,
characters, pointers, and the like.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Formatted-Output-Functions">12.12.7 Formatted Output Functions</a></td><td> </td><td align="left" valign="top"> Descriptions of the actual functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Dynamic-Output">12.12.8 Dynamically Allocating Formatted Output</a></td><td> </td><td align="left" valign="top"> Functions that allocate memory for the output.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Variable-Arguments-Output">12.12.9 Variable Arguments Output Functions</a></td><td> </td><td align="left" valign="top"> <code>vprintf</code> and friends.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Parsing-a-Template-String">12.12.10 Parsing a Template String</a></td><td> </td><td align="left" valign="top"> What kinds of args does a given template
call for?
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Example-of-Parsing">12.12.11 Example of Parsing a Template String</a></td><td> </td><td align="left" valign="top"> Sample program using <code>parse_printf_format</code>.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Customizing Printf
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#Registering-New-Conversions">12.13.1 Registering New Conversions</a></td><td> </td><td align="left" valign="top"> Using <code>register_printf_function</code>
to register a new output conversion.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Conversion-Specifier-Options">12.13.2 Conversion Specifier Options</a></td><td> </td><td align="left" valign="top"> The handler must be able to get
the options specified in the
template when it is called.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Defining-the-Output-Handler">12.13.3 Defining the Output Handler</a></td><td> </td><td align="left" valign="top"> Defining the handler and arginfo
functions that are passed as arguments
to <code>register_printf_function</code>.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Printf-Extension-Example">12.13.4 <code>printf</code> Extension Example</a></td><td> </td><td align="left" valign="top"> How to define a <code>printf</code>
handler function.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Predefined-Printf-Handlers">12.13.5 Predefined <code>printf</code> Handlers</a></td><td> </td><td align="left" valign="top"> Predefined <code>printf</code> handlers.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Formatted Input
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#Formatted-Input-Basics">12.14.1 Formatted Input Basics</a></td><td> </td><td align="left" valign="top"> Some basics to get you started.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Input-Conversion-Syntax">12.14.2 Input Conversion Syntax</a></td><td> </td><td align="left" valign="top"> Syntax of conversion specifications.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Table-of-Input-Conversions">12.14.3 Table of Input Conversions</a></td><td> </td><td align="left" valign="top"> Summary of input conversions and what they do.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Numeric-Input-Conversions">12.14.4 Numeric Input Conversions</a></td><td> </td><td align="left" valign="top"> Details of conversions for reading numbers.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#String-Input-Conversions">12.14.5 String Input Conversions</a></td><td> </td><td align="left" valign="top"> Details of conversions for reading strings.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Dynamic-String-Input">12.14.6 Dynamically Allocating String Conversions</a></td><td> </td><td align="left" valign="top"> String conversions that <code>malloc</code> the buffer.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Other-Input-Conversions">12.14.7 Other Input Conversions</a></td><td> </td><td align="left" valign="top"> Details of miscellaneous other conversions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Formatted-Input-Functions">12.14.8 Formatted Input Functions</a></td><td> </td><td align="left" valign="top"> Descriptions of the actual functions.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Variable-Arguments-Input">12.14.9 Variable Arguments Input Functions</a></td><td> </td><td align="left" valign="top"> <code>vscanf</code> and friends.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Stream Buffering
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#Buffering-Concepts">12.20.1 Buffering Concepts</a></td><td> </td><td align="left" valign="top"> Terminology is defined here.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Flushing-Buffers">12.20.2 Flushing Buffers</a></td><td> </td><td align="left" valign="top"> How to ensure that output buffers are flushed.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Controlling-Buffering">12.20.3 Controlling Which Kind of Buffering</a></td><td> </td><td align="left" valign="top"> How to specify what kind of buffering to use.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Other Kinds of Streams
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#String-Streams">12.21.1 String Streams</a></td><td> </td><td align="left" valign="top"> Streams that get data from or put data in
a string or memory buffer.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Custom-Streams">12.21.2 Programming Your Own Custom Streams</a></td><td> </td><td align="left" valign="top"> Defining your own streams with an arbitrary
input data source and/or output data sink.
</td></tr>
<tr><th colspan="3" align="left" valign="top"><pre class="menu-comment">
Custom Streams
</pre></th></tr><tr><td align="left" valign="top"><a href="libc_12.html#Streams-and-Cookies">12.21.2.1 Custom Streams and Cookies</a></td><td> </td><td align="left" valign="top"> The <em>cookie</em> records where to fetch or
store data that is read or written.
</td></tr>
<tr><td align="left" valign="top"><a href="libc_12.html#Hook-Functions">12.21.2.2 Custom Stream Hook Functions</a></td><td> </td><table class="menu" border="0" cellspacing="0">
How you should define the four <em>hook
<p><em> functions that a custom stream needs.
</em></p>
<p><em>Formatted Messages
</em></p>
<a href="libc_12.html#Printing-Formatted-Messages">12.22.1 Printing Formatted Messages</a> The <code>fmtmsg</code> function.
<a href="libc_12.html#Adding-Severity-Classes">12.22.2 Adding Severity Classes</a> Add more severity classes.
<a href="libc_12.html#Example">12.22.3 How to use <code>fmtmsg</code> and <code>addseverity</code></a> How to use <code>fmtmsg</code> and <code>addseverity</code>.
<p><em>Low-Level I/O
</em></p>
<a href="libc_13.html#Opening-and-Closing-Files">13.1 Opening and Closing Files</a> How to open and close file
descriptors.
<a href="libc_13.html#I_002fO-Primitives">13.2 Input and Output Primitives</a> Reading and writing data.
<a href="libc_13.html#File-Position-Primitive">13.3 Setting the File Position of a Descriptor</a> Setting a descriptor’s file
position.
<a href="libc_13.html#Descriptors-and-Streams">13.4 Descriptors and Streams</a> Converting descriptor to stream
or vice-versa.
<a href="libc_13.html#Stream_002fDescriptor-Precautions">13.5 Dangers of Mixing Streams and Descriptors</a> Precautions needed if you use both
descriptors and streams.
<a href="libc_13.html#Scatter_002dGather">13.6 Fast Scatter-Gather I/O</a> Fast I/O to discontinuous buffers.
<a href="libc_13.html#Memory_002dmapped-I_002fO">13.7 Memory-mapped I/O</a> Using files like memory.
<a href="libc_13.html#Waiting-for-I_002fO">13.8 Waiting for Input or Output</a> How to check for input or output
on multiple file descriptors.
<a href="libc_13.html#Synchronizing-I_002fO">13.9 Synchronizing I/O operations</a> Making sure all I/O actions completed.
<a href="libc_13.html#Asynchronous-I_002fO">13.10 Perform I/O Operations in Parallel</a> Perform I/O in parallel.
<a href="libc_13.html#Control-Operations">13.11 Control Operations on Files</a> Various other operations on file
descriptors.
<a href="libc_13.html#Duplicating-Descriptors">13.12 Duplicating Descriptors</a> Fcntl commands for duplicating
file descriptors.
<a href="libc_13.html#Descriptor-Flags">13.13 File Descriptor Flags</a> Fcntl commands for manipulating
flags associated with file
descriptors.
<a href="libc_13.html#File-Status-Flags">13.14 File Status Flags</a> Fcntl commands for manipulating
flags associated with open files.
<a href="libc_13.html#File-Locks">13.15 File Locks</a> Fcntl commands for implementing
file locking.
<a href="libc_13.html#Interrupt-Input">13.16 Interrupt-Driven Input</a> Getting an asynchronous signal when
input arrives.
<a href="libc_13.html#IOCTLs">13.17 Generic I/O Control operations</a> Generic I/O Control operations.
<p><em>Stream/Descriptor Precautions
</em></p>
<a href="libc_13.html#Linked-Channels">13.5.1 Linked Channels</a> Dealing with channels sharing a file position.
<a href="libc_13.html#Independent-Channels">13.5.2 Independent Channels</a> Dealing with separately opened, unlinked channels.
<a href="libc_13.html#Cleaning-Streams">13.5.3 Cleaning Streams</a> Cleaning a stream makes it safe to use
another channel.
<p><em>Asynchronous I/O
</em></p>
<a href="libc_13.html#Asynchronous-Reads_002fWrites">13.10.1 Asynchronous Read and Write Operations</a> Asynchronous Read and Write Operations.
<a href="libc_13.html#Status-of-AIO-Operations">13.10.2 Getting the Status of AIO Operations</a> Getting the Status of AIO Operations.
<a href="libc_13.html#Synchronizing-AIO-Operations">13.10.3 Getting into a Consistent State</a> Getting into a consistent state.
<a href="libc_13.html#Cancel-AIO-Operations">13.10.4 Cancellation of AIO Operations</a> Cancellation of AIO Operations.
<a href="libc_13.html#Configuration-of-AIO">13.10.5 How to optimize the AIO implementation</a> How to optimize the AIO implementation.
<p><em>File Status Flags
</em></p>
<a href="libc_13.html#Access-Modes">13.14.1 File Access Modes</a> Whether the descriptor can read or write.
<a href="libc_13.html#Open_002dtime-Flags">13.14.2 Open-time Flags</a> Details of <code>open</code>.
<a href="libc_13.html#Operating-Modes">13.14.3 I/O Operating Modes</a> Special modes to control I/O operations.
<a href="libc_13.html#Getting-File-Status-Flags">13.14.4 Getting and Setting File Status Flags</a> Fetching and changing these flags.
<p><em>File System Interface
</em></p>
<a href="libc_14.html#Working-Directory">14.1 Working Directory</a> This is used to resolve relative
file names.
<a href="libc_14.html#Accessing-Directories">14.2 Accessing Directories</a> Finding out what files a directory
contains.
<a href="libc_14.html#Working-with-Directory-Trees">14.3 Working with Directory Trees</a> Apply actions to all files or a selectable
subset of a directory hierarchy.
<a href="libc_14.html#Hard-Links">14.4 Hard Links</a> Adding alternate names to a file.
<a href="libc_14.html#Symbolic-Links">14.5 Symbolic Links</a> A file that “points to” a file name.
<a href="libc_14.html#Deleting-Files">14.6 Deleting Files</a> How to delete a file, and what that means.
<a href="libc_14.html#Renaming-Files">14.7 Renaming Files</a> Changing a file’s name.
<a href="libc_14.html#Creating-Directories">14.8 Creating Directories</a> A system call just for creating a directory.
<a href="libc_14.html#File-Attributes">14.9 File Attributes</a> Attributes of individual files.
<a href="libc_14.html#Making-Special-Files">14.10 Making Special Files</a> How to create special files.
<a href="libc_14.html#Temporary-Files">14.11 Temporary Files</a> Naming and creating temporary files.
<p><em>Accessing Directories
</em></p>
<a href="libc_14.html#Directory-Entries">14.2.1 Format of a Directory Entry</a> Format of one directory entry.
<a href="libc_14.html#Opening-a-Directory">14.2.2 Opening a Directory Stream</a> How to open a directory stream.
<a href="libc_14.html#Reading_002fClosing-Directory">14.2.3 Reading and Closing a Directory Stream</a> How to read directory entries from the stream.
<a href="libc_14.html#Simple-Directory-Lister">14.2.4 Simple Program to List a Directory</a> A very simple directory listing program.
<a href="libc_14.html#Random-Access-Directory">14.2.5 Random Access in a Directory Stream</a> Rereading part of the directory
already read with the same stream.
<a href="libc_14.html#Scanning-Directory-Content">14.2.6 Scanning the Content of a Directory</a> Get entries for user selected subset of
contents in given directory.
<a href="libc_14.html#Simple-Directory-Lister-Mark-II">14.2.7 Simple Program to List a Directory, Mark II</a> Revised version of the program.
<p><em>File Attributes
</em></p>
<a href="libc_14.html#Attribute-Meanings">14.9.1 The meaning of the File Attributes</a> The names of the file attributes,
and what their values mean.
<a href="libc_14.html#Reading-Attributes">14.9.2 Reading the Attributes of a File</a> How to read the attributes of a file.
<a href="libc_14.html#Testing-File-Type">14.9.3 Testing the Type of a File</a> Distinguishing ordinary files,
directories, links…
<a href="libc_14.html#File-Owner">14.9.4 File Owner</a> How ownership for new files is determined,
and how to change it.
<a href="libc_14.html#Permission-Bits">14.9.5 The Mode Bits for Access Permission</a> How information about a file’s access
mode is stored.
<a href="libc_14.html#Access-Permission">14.9.6 How Your Access to a File is Decided</a> How the system decides who can access a file.
<a href="libc_14.html#Setting-Permissions">14.9.7 Assigning File Permissions</a> How permissions for new files are assigned,
and how to change them.
<a href="libc_14.html#Testing-File-Access">14.9.8 Testing Permission to Access a File</a> How to find out if your process can
access a file.
<a href="libc_14.html#File-Times">14.9.9 File Times</a> About the time attributes of a file.
<a href="libc_14.html#File-Size">14.9.10 File Size</a> Manually changing the size of a file.
<p><em>Pipes and FIFOs
</em></p>
<a href="libc_15.html#Creating-a-Pipe">15.1 Creating a Pipe</a> Making a pipe with the <code>pipe</code> function.
<a href="libc_15.html#Pipe-to-a-Subprocess">15.2 Pipe to a Subprocess</a> Using a pipe to communicate with a
child process.
<a href="libc_15.html#FIFO-Special-Files">15.3 FIFO Special Files</a> Making a FIFO special file.
<a href="libc_15.html#Pipe-Atomicity">15.4 Atomicity of Pipe I/O</a> When pipe (or FIFO) I/O is atomic.
<p><em>Sockets
</em></p>
<a href="libc_16.html#Socket-Concepts">16.1 Socket Concepts</a> Basic concepts you need to know about.
<a href="libc_16.html#Communication-Styles">16.2 Communication Styles</a> Stream communication, datagrams and other styles.
<a href="libc_16.html#Socket-Addresses">16.3 Socket Addresses</a> How socket names (“addresses”) work.
<a href="libc_16.html#Interface-Naming">16.4 Interface Naming</a> Identifying specific network interfaces.
<a href="libc_16.html#Local-Namespace">16.5 The Local Namespace</a> Details about the local namespace.
<a href="libc_16.html#Internet-Namespace">16.6 The Internet Namespace</a> Details about the Internet namespace.
<a href="libc_16.html#Misc-Namespaces">16.7 Other Namespaces</a> Other namespaces not documented fully here.
<a href="libc_16.html#Open_002fClose-Sockets">16.8 Opening and Closing Sockets</a> Creating sockets and destroying them.
<a href="libc_16.html#Connections">16.9 Using Sockets with Connections</a> Operations on sockets with connection state.
<a href="libc_16.html#Datagrams">16.10 Datagram Socket Operations</a> Operations on datagram sockets.
<a href="libc_16.html#Inetd">16.11 The <code>inetd</code> Daemon</a> Inetd is a daemon that starts servers on request.
The most convenient way to write a server
is to make it work with Inetd.
<a href="libc_16.html#Socket-Options">16.12 Socket Options</a> Miscellaneous low-level socket options.
<a href="libc_16.html#Networks-Database">16.13 Networks Database</a> Accessing the database of network names.
<p><em>Socket Addresses
</em></p>
<a href="libc_16.html#Address-Formats">16.3.1 Address Formats</a> About <code>struct sockaddr</code>.
<a href="libc_16.html#Setting-Address">16.3.2 Setting the Address of a Socket</a> Binding an address to a socket.
<a href="libc_16.html#Reading-Address">16.3.3 Reading the Address of a Socket</a> Reading the address of a socket.
<p><em>Local Namespace
</em></p>
<a href="libc_16.html#Local-Namespace-Concepts">16.5.1 Local Namespace Concepts</a> What you need to understand.
<a href="libc_16.html#Local-Namespace-Details">16.5.2 Details of Local Namespace</a> Address format, symbolic names, etc.
<a href="libc_16.html#Local-Socket-Example">16.5.3 Example of Local-Namespace Sockets</a> Example of creating a socket.
<p><em>Internet Namespace
</em></p>
<a href="libc_16.html#Internet-Address-Formats">16.6.1 Internet Socket Address Formats</a> How socket addresses are specified in the
Internet namespace.
<a href="libc_16.html#Host-Addresses">16.6.2 Host Addresses</a> All about host addresses of Internet host.
<a href="libc_16.html#Protocols-Database">16.6.6 Protocols Database</a> Referring to protocols by name.
<a href="libc_16.html#Ports">16.6.3 Internet Ports</a> Internet port numbers.
<a href="libc_16.html#Services-Database">16.6.4 The Services Database</a> Ports may have symbolic names.
<a href="libc_16.html#Byte-Order">16.6.5 Byte Order Conversion</a> Different hosts may use different byte
ordering conventions; you need to
canonicalize host address and port number.
<a href="libc_16.html#Inet-Example">16.6.7 Internet Socket Example</a> Putting it all together.
<p><em>Host Addresses
</em></p>
<a href="libc_16.html#Abstract-Host-Addresses">16.6.2.1 Internet Host Addresses</a> What a host number consists of.
<a href="libc_16.html#Host-Address-Data-Type">16.6.2.2 Host Address Data Type</a> Data type for a host number.
<a href="libc_16.html#Host-Address-Functions">16.6.2.3 Host Address Functions</a> Functions to operate on them.
<a href="libc_16.html#Host-Names">16.6.2.4 Host Names</a> Translating host names to host numbers.
<p><em>Open/Close Sockets
</em></p>
<a href="libc_16.html#Creating-a-Socket">16.8.1 Creating a Socket</a> How to open a socket.
<a href="libc_16.html#Closing-a-Socket">16.8.2 Closing a Socket</a> How to close a socket.
<a href="libc_16.html#Socket-Pairs">16.8.3 Socket Pairs</a> These are created like pipes.
<p><em>Connections
</em></p>
<a href="libc_16.html#Connecting">16.9.1 Making a Connection</a> What the client program must do.
<a href="libc_16.html#Listening">16.9.2 Listening for Connections</a> How a server program waits for requests.
<a href="libc_16.html#Accepting-Connections">16.9.3 Accepting Connections</a> What the server does when it gets a request.
<a href="libc_16.html#Who-is-Connected">16.9.4 Who is Connected to Me?</a> Getting the address of the
other side of a connection.
<a href="libc_16.html#Transferring-Data">16.9.5 Transferring Data</a> How to send and receive data.
<a href="libc_16.html#Byte-Stream-Example">16.9.6 Byte Stream Socket Example</a> An example program: a client for communicating
over a byte stream socket in the Internet namespace.
<a href="libc_16.html#Server-Example">16.9.7 Byte Stream Connection Server Example</a> A corresponding server program.
<a href="libc_16.html#Out_002dof_002dBand-Data">16.9.8 Out-of-Band Data</a> This is an advanced feature.
<p><em>Transferring Data
</em></p>
<a href="libc_16.html#Sending-Data">16.9.5.1 Sending Data</a> Sending data with <code>send</code>.
<a href="libc_16.html#Receiving-Data">16.9.5.2 Receiving Data</a> Reading data with <code>recv</code>.
<a href="libc_16.html#Socket-Data-Options">16.9.5.3 Socket Data Options</a> Using <code>send</code> and <code>recv</code>.
<p><em>Datagrams
</em></p>
<a href="libc_16.html#Sending-Datagrams">16.10.1 Sending Datagrams</a> Sending packets on a datagram socket.
<a href="libc_16.html#Receiving-Datagrams">16.10.2 Receiving Datagrams</a> Receiving packets on a datagram socket.
<a href="libc_16.html#Datagram-Example">16.10.3 Datagram Socket Example</a> An example program: packets sent over a
datagram socket in the local namespace.
<a href="libc_16.html#Example-Receiver">16.10.4 Example of Reading Datagrams</a> Another program, that receives those packets.
<p><em>Inetd
</em></p>
<a href="libc_16.html#Inetd-Servers">16.11.1 <code>inetd</code> Servers</a>
<a href="libc_16.html#Configuring-Inetd">16.11.2 Configuring <code>inetd</code></a>
<p><em>Socket Options
</em></p>
<a href="libc_16.html#Socket-Option-Functions">16.12.1 Socket Option Functions</a> The basic functions for setting and getting
socket options.
<a href="libc_16.html#Socket_002dLevel-Options">16.12.2 Socket-Level Options</a> Details of the options at the socket level.
<p><em>Low-Level Terminal Interface
</em></p>
<a href="libc_17.html#Is-It-a-Terminal">17.1 Identifying Terminals</a> How to determine if a file is a terminal
device, and what its name is.
<a href="libc_17.html#I_002fO-Queues">17.2 I/O Queues</a> About flow control and typeahead.
<a href="libc_17.html#Canonical-or-Not">17.3 Two Styles of Input: Canonical or Not</a> Two basic styles of input processing.
<a href="libc_17.html#Terminal-Modes">17.4 Terminal Modes</a> How to examine and modify flags controlling
details of terminal I/O: echoing,
signals, editing. Posix.
<a href="libc_17.html#BSD-Terminal-Modes">17.5 BSD Terminal Modes</a> BSD compatible terminal mode setting
<a href="libc_17.html#Line-Control">17.6 Line Control Functions</a> Sending break sequences, clearing
terminal buffers …
<a href="libc_17.html#Noncanon-Example">17.7 Noncanonical Mode Example</a> How to read single characters without echo.
<a href="libc_17.html#Pseudo_002dTerminals">17.8 Pseudo-Terminals</a> How to open a pseudo-terminal.
<p><em>Terminal Modes
</em></p>
<a href="libc_17.html#Mode-Data-Types">17.4.1 Terminal Mode Data Types</a> The data type <code>struct termios</code> and
related types.
<a href="libc_17.html#Mode-Functions">17.4.2 Terminal Mode Functions</a> Functions to read and set the terminal
attributes.
<a href="libc_17.html#Setting-Modes">17.4.3 Setting Terminal Modes Properly</a> The right way to set terminal attributes
reliably.
<a href="libc_17.html#Input-Modes">17.4.4 Input Modes</a> Flags controlling low-level input handling.
<a href="libc_17.html#Output-Modes">17.4.5 Output Modes</a> Flags controlling low-level output handling.
<a href="libc_17.html#Control-Modes">17.4.6 Control Modes</a> Flags controlling serial port behavior.
<a href="libc_17.html#Local-Modes">17.4.7 Local Modes</a> Flags controlling high-level input handling.
<a href="libc_17.html#Line-Speed">17.4.8 Line Speed</a> How to read and set the terminal line speed.
<a href="libc_17.html#Special-Characters">17.4.9 Special Characters</a> Characters that have special effects,
and how to change them.
<a href="libc_17.html#Noncanonical-Input">17.4.10 Noncanonical Input</a> Controlling how long to wait for input.
<p><em>Special Characters
</em></p>
<a href="libc_17.html#Editing-Characters">17.4.9.1 Characters for Input Editing</a> Special characters that terminate lines and
delete text, and other editing functions.
<a href="libc_17.html#Signal-Characters">17.4.9.2 Characters that Cause Signals</a> Special characters that send or raise signals
to or for certain classes of processes.
<a href="libc_17.html#Start_002fStop-Characters">17.4.9.3 Special Characters for Flow Control</a> Special characters that suspend or resume
suspended output.
<a href="libc_17.html#Other-Special">17.4.9.4 Other Special Characters</a> Other special characters for BSD systems:
they can discard output, and print status.
<p><em>Pseudo-Terminals
</em></p>
<a href="libc_17.html#Allocation">17.8.1 Allocating Pseudo-Terminals</a> Allocating a pseudo terminal.
<a href="libc_17.html#Pseudo_002dTerminal-Pairs">17.8.2 Opening a Pseudo-Terminal Pair</a> How to open both sides of a
pseudo-terminal in a single operation.
<p><em>Syslog
</em></p>
<a href="libc_18.html#Overview-of-Syslog">18.1 Overview of Syslog</a> Overview of a system’s Syslog facility
<a href="libc_18.html#Submitting-Syslog-Messages">18.2 Submitting Syslog Messages</a> Functions to submit messages to Syslog
<p><em>Submitting Syslog Messages
</em></p>
<a href="libc_18.html#openlog">18.2.1 openlog</a> Open connection to Syslog
<a href="libc_18.html#syslog_003b-vsyslog">18.2.2 syslog, vsyslog</a> Submit message to Syslog
<a href="libc_18.html#closelog">18.2.3 closelog</a> Close connection to Syslog
<a href="libc_18.html#setlogmask">18.2.4 setlogmask</a> Cause certain messages to be ignored
<a href="libc_18.html#Syslog-Example">18.2.5 Syslog Example</a> Example of all of the above
<p><em>Mathematics
</em></p>
<a href="libc_19.html#Mathematical-Constants">19.1 Predefined Mathematical Constants</a> Precise numeric values for often-used
constants.
<a href="libc_19.html#Trig-Functions">19.2 Trigonometric Functions</a> Sine, cosine, tangent, and friends.
<a href="libc_19.html#Inverse-Trig-Functions">19.3 Inverse Trigonometric Functions</a> Arcsine, arccosine, etc.
<a href="libc_19.html#Exponents-and-Logarithms">19.4 Exponentiation and Logarithms</a> Also pow and sqrt.
<a href="libc_19.html#Hyperbolic-Functions">19.5 Hyperbolic Functions</a> sinh, cosh, tanh, etc.
<a href="libc_19.html#Special-Functions">19.6 Special Functions</a> Bessel, gamma, erf.
<a href="libc_19.html#Errors-in-Math-Functions">19.7 Known Maximum Errors in Math Functions</a> Known Maximum Errors in Math Functions.
<a href="libc_19.html#Pseudo_002dRandom-Numbers">19.8 Pseudo-Random Numbers</a> Functions for generating pseudo-random
numbers.
<a href="libc_19.html#FP-Function-Optimizations">19.9 Is Fast Code or Small Code preferred?</a> Fast code or small code.
<p><em>Pseudo-Random Numbers
</em></p>
<a href="libc_19.html#ISO-Random">19.8.1 ISO C Random Number Functions</a> <code>rand</code> and friends.
<a href="libc_19.html#BSD-Random">19.8.2 BSD Random Number Functions</a> <code>random</code> and friends.
<a href="libc_19.html#SVID-Random">19.8.3 SVID Random Number Function</a> <code>drand48</code> and friends.
<p><em>Arithmetic
</em></p>
<a href="libc_20.html#Integers">20.1 Integers</a> Basic integer types and concepts
<a href="libc_20.html#Integer-Division">20.2 Integer Division</a> Integer division with guaranteed rounding.
<a href="libc_20.html#Floating-Point-Numbers">20.3 Floating Point Numbers</a> Basic concepts. IEEE 754.
<a href="libc_20.html#Floating-Point-Classes">20.4 Floating-Point Number Classification Functions</a> The five kinds of floating-point number.
<a href="libc_20.html#Floating-Point-Errors">20.5 Errors in Floating-Point Calculations</a> When something goes wrong in a calculation.
<a href="libc_20.html#Rounding">20.6 Rounding Modes</a> Controlling how results are rounded.
<a href="libc_20.html#Control-Functions">20.7 Floating-Point Control Functions</a> Saving and restoring the FPU’s state.
<a href="libc_20.html#Arithmetic-Functions">20.8 Arithmetic Functions</a> Fundamental operations provided by the library.
<a href="libc_20.html#Complex-Numbers">20.9 Complex Numbers</a> The types. Writing complex constants.
<a href="libc_20.html#Operations-on-Complex">20.10 Projections, Conjugates, and Decomposing of Complex Numbers</a> Projection, conjugation, decomposition.
<a href="libc_20.html#Parsing-of-Numbers">20.11 Parsing of Numbers</a> Converting strings to numbers.
<a href="libc_20.html#System-V-Number-Conversion">20.12 Old-fashioned System V number-to-string functions</a> An archaic way to convert numbers to strings.
<p><em>Floating Point Errors
</em></p>
<a href="libc_20.html#FP-Exceptions">20.5.1 FP Exceptions</a> IEEE 754 math exceptions and how to detect them.
<a href="libc_20.html#Infinity-and-NaN">20.5.2 Infinity and NaN</a> Special values returned by calculations.
<a href="libc_20.html#Status-bit-operations">20.5.3 Examining the FPU status word</a> Checking for exceptions after the fact.
<a href="libc_20.html#Math-Error-Reporting">20.5.4 Error Reporting by Mathematical Functions</a> How the math functions report errors.
<p><em>Arithmetic Functions
</em></p>
<a href="libc_20.html#Absolute-Value">20.8.1 Absolute Value</a> Absolute values of integers and floats.
<a href="libc_20.html#Normalization-Functions">20.8.2 Normalization Functions</a> Extracting exponents and putting them back.
<a href="libc_20.html#Rounding-Functions">20.8.3 Rounding Functions</a> Rounding floats to integers.
<a href="libc_20.html#Remainder-Functions">20.8.4 Remainder Functions</a> Remainders on division, precisely defined.
<a href="libc_20.html#FP-Bit-Twiddling">20.8.5 Setting and modifying single bits of FP values</a> Sign bit adjustment. Adding epsilon.
<a href="libc_20.html#FP-Comparison-Functions">20.8.6 Floating-Point Comparison Functions</a> Comparisons without risk of exceptions.
<a href="libc_20.html#Misc-FP-Arithmetic">20.8.7 Miscellaneous FP arithmetic functions</a> Max, min, positive difference, multiply-add.
<p><em>Parsing of Numbers
</em></p>
<a href="libc_20.html#Parsing-of-Integers">20.11.1 Parsing of Integers</a> Functions for conversion of integer values.
<a href="libc_20.html#Parsing-of-Floats">20.11.2 Parsing of Floats</a> Functions for conversion of floating-point
values.
<p><em>Date and Time
</em></p>
<a href="libc_21.html#Time-Basics">21.1 Time Basics</a> Concepts and definitions.
<a href="libc_21.html#Elapsed-Time">21.2 Elapsed Time</a> Data types to represent elapsed times
<a href="libc_21.html#Processor-And-CPU-Time">21.3 Processor And CPU Time</a> Time a program has spent executing.
<a href="libc_21.html#Calendar-Time">21.4 Calendar Time</a> Manipulation of “real” dates and times.
<a href="libc_21.html#Setting-an-Alarm">21.5 Setting an Alarm</a> Sending a signal after a specified time.
<a href="libc_21.html#Sleeping">21.6 Sleeping</a> Waiting for a period of time.
<p><em>Processor And CPU Time
</em></p>
<a href="libc_21.html#CPU-Time">21.3.1 CPU Time Inquiry</a> The <code>clock</code> function.
<a href="libc_21.html#Processor-Time">21.3.2 Processor Time Inquiry</a> The <code>times</code> function.
<p><em>Calendar Time
</em></p>
<a href="libc_21.html#Simple-Calendar-Time">21.4.1 Simple Calendar Time</a> Facilities for manipulating calendar time.
<a href="libc_21.html#High_002dResolution-Calendar">21.4.2 High-Resolution Calendar</a> A time representation with greater precision.
<a href="libc_21.html#Broken_002ddown-Time">21.4.3 Broken-down Time</a> Facilities for manipulating local time.
<a href="libc_21.html#High-Accuracy-Clock">21.4.4 High Accuracy Clock</a> Maintaining a high accuracy system clock.
<a href="libc_21.html#Formatting-Calendar-Time">21.4.5 Formatting Calendar Time</a> Converting times to strings.
<a href="libc_21.html#Parsing-Date-and-Time">21.4.6 Convert textual time and date information back</a> Convert textual time and date information back
into broken-down time values.
<a href="libc_21.html#TZ-Variable">21.4.7 Specifying the Time Zone with <code>TZ</code></a> How users specify the time zone.
<a href="libc_21.html#Time-Zone-Functions">21.4.8 Functions and Variables for Time Zones</a> Functions to examine or specify the time zone.
<a href="libc_21.html#Time-Functions-Example">21.4.9 Time Functions Example</a> An example program showing use of some of
the time functions.
<p><em>Parsing Date and Time
</em></p>
<a href="libc_21.html#Low_002dLevel-Time-String-Parsing">21.4.6.1 Interpret string according to given format</a> Interpret string according to given format.
<a href="libc_21.html#General-Time-String-Parsing">21.4.6.2 A More User-friendly Way to Parse Times and Dates</a> User-friendly function to parse data and
time strings.
<p><em>Resource Usage And Limitation
</em></p>
<a href="libc_22.html#Resource-Usage">22.1 Resource Usage</a> Measuring various resources used.
<a href="libc_22.html#Limits-on-Resources">22.2 Limiting Resource Usage</a> Specifying limits on resource usage.
<a href="libc_22.html#Priority">22.3 Process CPU Priority And Scheduling</a> Reading or setting process run priority.
<a href="libc_22.html#Memory-Resources">22.4 Querying memory available resources</a> Querying memory available resources.
<a href="libc_22.html#Processor-Resources">22.5 Learn about the processors available</a> Learn about the processors available.
<p><em>Priority
</em></p>
<a href="libc_22.html#Absolute-Priority">22.3.1 Absolute Priority</a> The first tier of priority. Posix
<a href="libc_22.html#Realtime-Scheduling">22.3.2 Realtime Scheduling</a> Scheduling among the process nobility
<a href="libc_22.html#Basic-Scheduling-Functions">22.3.3 Basic Scheduling Functions</a> Get/set scheduling policy, priority
<a href="libc_22.html#Traditional-Scheduling">22.3.4 Traditional Scheduling</a> Scheduling among the vulgar masses
<a href="libc_22.html#CPU-Affinity">22.3.5 Limiting execution to certain CPUs</a> Limiting execution to certain CPUs
<p><em>Traditional Scheduling
</em></p>
<a href="libc_22.html#Traditional-Scheduling-Intro">22.3.4.1 Introduction To Traditional Scheduling</a>
<a href="libc_22.html#Traditional-Scheduling-Functions">22.3.4.2 Functions For Traditional Scheduling</a>
<p><em>Memory Resources
</em></p>
<a href="libc_22.html#Memory-Subsystem">22.4.1 Overview about traditional Unix memory handling</a> Overview about traditional Unix memory handling.
<a href="libc_22.html#Query-Memory-Parameters">22.4.2 How to get information about the memory subsystem?</a> How to get information about the memory
subsystem?
<p><em>Non-Local Exits
</em></p>
<a href="libc_23.html#Non_002dLocal-Intro">23.1 Introduction to Non-Local Exits</a> When and how to use these facilities.
<a href="libc_23.html#Non_002dLocal-Details">23.2 Details of Non-Local Exits</a> Functions for non-local exits.
<a href="libc_23.html#Non_002dLocal-Exits-and-Signals">23.3 Non-Local Exits and Signals</a> Portability issues.
<a href="libc_23.html#System-V-contexts">23.4 Complete Context Control</a> Complete context control a la System V.
<p><em>Signal Handling
</em></p>
<a href="libc_24.html#Concepts-of-Signals">24.1 Basic Concepts of Signals</a> Introduction to the signal facilities.
<a href="libc_24.html#Standard-Signals">24.2 Standard Signals</a> Particular kinds of signals with
standard names and meanings.
<a href="libc_24.html#Signal-Actions">24.3 Specifying Signal Actions</a> Specifying what happens when a
particular signal is delivered.
<a href="libc_24.html#Defining-Handlers">24.4 Defining Signal Handlers</a> How to write a signal handler function.
<a href="libc_24.html#Interrupted-Primitives">24.5 Primitives Interrupted by Signals</a> Signal handlers affect use of <code>open</code>,
<code>read</code>, <code>write</code> and other functions.
<a href="libc_24.html#Generating-Signals">24.6 Generating Signals</a> How to send a signal to a process.
<a href="libc_24.html#Blocking-Signals">24.7 Blocking Signals</a> Making the system hold signals temporarily.
<a href="libc_24.html#Waiting-for-a-Signal">24.8 Waiting for a Signal</a> Suspending your program until a signal
arrives.
<a href="libc_24.html#Signal-Stack">24.9 Using a Separate Signal Stack</a> Using a Separate Signal Stack.
<a href="libc_24.html#BSD-Signal-Handling">24.10 BSD Signal Handling</a> Additional functions for backward
compatibility with BSD.
<p><em>Concepts of Signals
</em></p>
<a href="libc_24.html#Kinds-of-Signals">24.1.1 Some Kinds of Signals</a> Some examples of what can cause a signal.
<a href="libc_24.html#Signal-Generation">24.1.2 Concepts of Signal Generation</a> Concepts of why and how signals occur.
<a href="libc_24.html#Delivery-of-Signal">24.1.3 How Signals Are Delivered</a> Concepts of what a signal does to the
process.
<p><em>Standard Signals
</em></p>
<a href="libc_24.html#Program-Error-Signals">24.2.1 Program Error Signals</a> Used to report serious program errors.
<a href="libc_24.html#Termination-Signals">24.2.2 Termination Signals</a> Used to interrupt and/or terminate the
program.
<a href="libc_24.html#Alarm-Signals">24.2.3 Alarm Signals</a> Used to indicate expiration of timers.
<a href="libc_24.html#Asynchronous-I_002fO-Signals">24.2.4 Asynchronous I/O Signals</a> Used to indicate input is available.
<a href="libc_24.html#Job-Control-Signals">24.2.5 Job Control Signals</a> Signals used to support job control.
<a href="libc_24.html#Operation-Error-Signals">24.2.6 Operation Error Signals</a> Used to report operational system errors.
<a href="libc_24.html#Miscellaneous-Signals">24.2.7 Miscellaneous Signals</a> Miscellaneous Signals.
<a href="libc_24.html#Signal-Messages">24.2.8 Signal Messages</a> Printing a message describing a signal.
<p><em>Signal Actions
</em></p>
<a href="libc_24.html#Basic-Signal-Handling">24.3.1 Basic Signal Handling</a> The simple <code>signal</code> function.
<a href="libc_24.html#Advanced-Signal-Handling">24.3.2 Advanced Signal Handling</a> The more powerful <code>sigaction</code> function.
<a href="libc_24.html#Signal-and-Sigaction">24.3.3 Interaction of <code>signal</code> and <code>sigaction</code></a> How those two functions interact.
<a href="libc_24.html#Sigaction-Function-Example">24.3.4 <code>sigaction</code> Function Example</a> An example of using the sigaction function.
<a href="libc_24.html#Flags-for-Sigaction">24.3.5 Flags for <code>sigaction</code></a> Specifying options for signal handling.
<a href="libc_24.html#Initial-Signal-Actions">24.3.6 Initial Signal Actions</a> How programs inherit signal actions.
<p><em>Defining Handlers
</em></p>
<a href="libc_24.html#Handler-Returns">24.4.1 Signal Handlers that Return</a> Handlers that return normally, and what
this means.
<a href="libc_24.html#Termination-in-Handler">24.4.2 Handlers That Terminate the Process</a> How handler functions terminate a program.
<a href="libc_24.html#Longjmp-in-Handler">24.4.3 Nonlocal Control Transfer in Handlers</a> Nonlocal transfer of control out of a
signal handler.
<a href="libc_24.html#Signals-in-Handler">24.4.4 Signals Arriving While a Handler Runs</a> What happens when signals arrive while
the handler is already occupied.
<a href="libc_24.html#Merged-Signals">24.4.5 Signals Close Together Merge into One</a> When a second signal arrives before the
first is handled.
<a href="libc_24.html#Nonreentrancy">24.4.6 Signal Handling and Nonreentrant Functions</a> Do not call any functions unless you know they
are reentrant with respect to signals.
<a href="libc_24.html#Atomic-Data-Access">24.4.7 Atomic Data Access and Signal Handling</a> A single handler can run in the middle of
reading or writing a single object.
<p><em>Atomic Data Access
</em></p>
<a href="libc_24.html#Non_002datomic-Example">24.4.7.1 Problems with Non-Atomic Access</a> A program illustrating interrupted access.
<a href="libc_24.html#Atomic-Types">24.4.7.2 Atomic Types</a> Data types that guarantee no interruption.
<a href="libc_24.html#Atomic-Usage">24.4.7.3 Atomic Usage Patterns</a> Proving that interruption is harmless.
<p><em>Generating Signals
</em></p>
<a href="libc_24.html#Signaling-Yourself">24.6.1 Signaling Yourself</a> A process can send a signal to itself.
<a href="libc_24.html#Signaling-Another-Process">24.6.2 Signaling Another Process</a> Send a signal to another process.
<a href="libc_24.html#Permission-for-kill">24.6.3 Permission for using <code>kill</code></a> Permission for using <code>kill</code>.
<a href="libc_24.html#Kill-Example">24.6.4 Using <code>kill</code> for Communication</a> Using <code>kill</code> for Communication.
<p><em>Blocking Signals
</em></p>
<a href="libc_24.html#Why-Block">24.7.1 Why Blocking Signals is Useful</a> The purpose of blocking signals.
<a href="libc_24.html#Signal-Sets">24.7.2 Signal Sets</a> How to specify which signals to
block.
<a href="libc_24.html#Process-Signal-Mask">24.7.3 Process Signal Mask</a> Blocking delivery of signals to your
process during normal execution.
<a href="libc_24.html#Testing-for-Delivery">24.7.4 Blocking to Test for Delivery of a Signal</a> Blocking to Test for Delivery of
a Signal.
<a href="libc_24.html#Blocking-for-Handler">24.7.5 Blocking Signals for a Handler</a> Blocking additional signals while a
handler is being run.
<a href="libc_24.html#Checking-for-Pending-Signals">24.7.6 Checking for Pending Signals</a> Checking for Pending Signals
<a href="libc_24.html#Remembering-a-Signal">24.7.7 Remembering a Signal to Act On Later</a> How you can get almost the same
effect as blocking a signal, by
handling it and setting a flag
to be tested later.
<p><em>Waiting for a Signal
</em></p>
<a href="libc_24.html#Using-Pause">24.8.1 Using <code>pause</code></a> The simple way, using <code>pause</code>.
<a href="libc_24.html#Pause-Problems">24.8.2 Problems with <code>pause</code></a> Why the simple way is often not very good.
<a href="libc_24.html#Sigsuspend">24.8.3 Using <code>sigsuspend</code></a> Reliably waiting for a specific signal.
<p><em>BSD Signal Handling
</em></p>
<a href="libc_24.html#BSD-Handler">24.10.1 BSD Function to Establish a Handler</a> BSD Function to Establish a Handler.
<a href="libc_24.html#Blocking-in-BSD">24.10.2 BSD Functions for Blocking Signals</a> BSD Functions for Blocking Signals.
<p><em>Program Basics
</em></p>
<a href="libc_25.html#Program-Arguments">25.1 Program Arguments</a> Parsing your program’s command-line arguments.
<a href="libc_25.html#Environment-Variables">25.4 Environment Variables</a> Less direct parameters affecting your program
<a href="libc_25.html#System-Calls">25.5 System Calls</a> Requesting service from the system
<a href="libc_25.html#Program-Termination">25.6 Program Termination</a> Telling the system you’re done; return status
<p><em>Program Arguments
</em></p>
<a href="libc_25.html#Argument-Syntax">25.1.1 Program Argument Syntax Conventions</a> By convention, options start with a hyphen.
<a href="libc_25.html#Parsing-Program-Arguments">25.1.2 Parsing Program Arguments</a> Ways to parse program options and arguments.
<p><em>Parsing Program Arguments
</em></p>
<a href="libc_25.html#Getopt">25.2 Parsing program options using <code>getopt</code></a> Parsing program options using <code>getopt</code>.
<a href="libc_25.html#Argp">25.3 Parsing Program Options with Argp</a> Parsing program options using <code>argp_parse</code>.
<a href="libc_25.html#Suboptions">25.3.12.1 Parsing of Suboptions</a> Some programs need more detailed options.
<a href="libc_25.html#Suboptions-Example">25.3.13 Parsing of Suboptions Example</a> This shows how it could be done for <code>mount</code>.
<p><em>Environment Variables
</em></p>
<a href="libc_25.html#Environment-Access">25.4.1 Environment Access</a> How to get and set the values of
environment variables.
<a href="libc_25.html#Standard-Environment">25.4.2 Standard Environment Variables</a> These environment variables have
standard interpretations.
<p><em>Program Termination
</em></p>
<a href="libc_25.html#Normal-Termination">25.6.1 Normal Termination</a> If a program calls <code>exit</code>, a
process terminates normally.
<a href="libc_25.html#Exit-Status">25.6.2 Exit Status</a> The <code>exit status</code> provides information
about why the process terminated.
<a href="libc_25.html#Cleanups-on-Exit">25.6.3 Cleanups on Exit</a> A process can run its own cleanup
functions upon normal termination.
<a href="libc_25.html#Aborting-a-Program">25.6.4 Aborting a Program</a> The <code>abort</code> function causes
abnormal program termination.
<a href="libc_25.html#Termination-Internals">25.6.5 Termination Internals</a> What happens when a process terminates.
<p><em>Processes
</em></p>
<a href="libc_26.html#Running-a-Command">26.1 Running a Command</a> The easy way to run another program.
<a href="libc_26.html#Process-Creation-Concepts">26.2 Process Creation Concepts</a> An overview of the hard way to do it.
<a href="libc_26.html#Process-Identification">26.3 Process Identification</a> How to get the process ID of a process.
<a href="libc_26.html#Creating-a-Process">26.4 Creating a Process</a> How to fork a child process.
<a href="libc_26.html#Executing-a-File">26.5 Executing a File</a> How to make a process execute another program.
<a href="libc_26.html#Process-Completion">26.6 Process Completion</a> How to tell when a child process has completed.
<a href="libc_26.html#Process-Completion-Status">26.7 Process Completion Status</a> How to interpret the status value
returned from a child process.
<a href="libc_26.html#BSD-Wait-Functions">26.8 BSD Process Wait Functions</a> More functions, for backward compatibility.
<a href="libc_26.html#Process-Creation-Example">26.9 Process Creation Example</a> A complete example program.
<p><em>Job Control
</em></p>
<a href="libc_27.html#Concepts-of-Job-Control">27.1 Concepts of Job Control</a> Jobs can be controlled by a shell.
<a href="libc_27.html#Job-Control-is-Optional">27.2 Job Control is Optional</a> Not all POSIX systems support job control.
<a href="libc_27.html#Controlling-Terminal">27.3 Controlling Terminal of a Process</a> How a process gets its controlling terminal.
<a href="libc_27.html#Access-to-the-Terminal">27.4 Access to the Controlling Terminal</a> How processes share the controlling terminal.
<a href="libc_27.html#Orphaned-Process-Groups">27.5 Orphaned Process Groups</a> Jobs left after the user logs out.
<a href="libc_27.html#Implementing-a-Shell">27.6 Implementing a Job Control Shell</a> What a shell must do to implement job control.
<a href="libc_27.html#Functions-for-Job-Control">27.7 Functions for Job Control</a> Functions to control process groups.
<p><em>Implementing a Shell
</em></p>
<a href="libc_27.html#Data-Structures">27.6.1 Data Structures for the Shell</a> Introduction to the sample shell.
<a href="libc_27.html#Initializing-the-Shell">27.6.2 Initializing the Shell</a> What the shell must do to take
responsibility for job control.
<a href="libc_27.html#Launching-Jobs">27.6.3 Launching Jobs</a> Creating jobs to execute commands.
<a href="libc_27.html#Foreground-and-Background">27.6.4 Foreground and Background</a> Putting a job in foreground of background.
<a href="libc_27.html#Stopped-and-Terminated-Jobs">27.6.5 Stopped and Terminated Jobs</a> Reporting job status.
<a href="libc_27.html#Continuing-Stopped-Jobs">27.6.6 Continuing Stopped Jobs</a> How to continue a stopped job in
the foreground or background.
<a href="libc_27.html#Missing-Pieces">27.6.7 The Missing Pieces</a> Other parts of the shell.
<p><em>Functions for Job Control
</em></p>
<a href="libc_27.html#Identifying-the-Terminal">27.7.1 Identifying the Controlling Terminal</a> Determining the controlling terminal’s name.
<a href="libc_27.html#Process-Group-Functions">27.7.2 Process Group Functions</a> Functions for manipulating process groups.
<a href="libc_27.html#Terminal-Access-Functions">27.7.3 Functions for Controlling Terminal Access</a> Functions for controlling terminal access.
<p><em>Name Service Switch
</em></p>
<a href="libc_28.html#NSS-Basics">28.1 NSS Basics</a> What is this NSS good for.
<a href="libc_28.html#NSS-Configuration-File">28.2 The NSS Configuration File</a> Configuring NSS.
<a href="libc_28.html#NSS-Module-Internals">28.3 NSS Module Internals</a> How does it work internally.
<a href="libc_28.html#Extending-NSS">28.4 Extending NSS</a> What to do to add services or databases.
<p><em>NSS Configuration File
</em></p>
<a href="libc_28.html#Services-in-the-NSS-configuration">28.2.1 Services in the NSS configuration File</a> Service names in the NSS configuration.
<a href="libc_28.html#Actions-in-the-NSS-configuration">28.2.2 Actions in the NSS configuration</a> React appropriately to the lookup result.
<a href="libc_28.html#Notes-on-NSS-Configuration-File">28.2.3 Notes on the NSS Configuration File</a> Things to take care about while
configuring NSS.
<p><em>NSS Module Internals
</em></p>
<a href="libc_28.html#NSS-Module-Names">28.3.1 The Naming Scheme of the NSS Modules</a> Construction of the interface function of
the NSS modules.
<a href="libc_28.html#NSS-Modules-Interface">28.3.2 The Interface of the Function in NSS Modules</a> Programming interface in the NSS module
functions.
<p><em>Extending NSS
</em></p>
<a href="libc_28.html#Adding-another-Service-to-NSS">28.4.1 Adding another Service to NSS</a> What is to do to add a new service.
<a href="libc_28.html#NSS-Module-Function-Internals">28.4.2 Internals of the NSS Module Functions</a> Guidelines for writing new NSS
service functions.
<p><em>Users and Groups
</em></p>
<a href="libc_29.html#User-and-Group-IDs">29.1 User and Group IDs</a> Each user has a unique numeric ID;
likewise for groups.
<a href="libc_29.html#Process-Persona">29.2 The Persona of a Process</a> The user IDs and group IDs of a process.
<a href="libc_29.html#Why-Change-Persona">29.3 Why Change the Persona of a Process?</a> Why a program might need to change
its user and/or group IDs.
<a href="libc_29.html#How-Change-Persona">29.4 How an Application Can Change Persona</a> Changing the user and group IDs.
<a href="libc_29.html#Reading-Persona">29.5 Reading the Persona of a Process</a> How to examine the user and group IDs.
<a href="libc_29.html#Setting-User-ID">29.6 Setting the User ID</a> Functions for setting the user ID.
<a href="libc_29.html#Setting-Groups">29.7 Setting the Group IDs</a> Functions for setting the group IDs.
<a href="libc_29.html#Enable_002fDisable-Setuid">29.8 Enabling and Disabling Setuid Access</a> Turning setuid access on and off.
<a href="libc_29.html#Setuid-Program-Example">29.9 Setuid Program Example</a> The pertinent parts of one sample program.
<a href="libc_29.html#Tips-for-Setuid">29.10 Tips for Writing Setuid Programs</a> How to avoid granting unlimited access.
<a href="libc_29.html#Who-Logged-In">29.11 Identifying Who Logged In</a> Getting the name of the user who logged in,
or of the real user ID of the current process.
<a href="libc_29.html#User-Accounting-Database">29.12 The User Accounting Database</a> Keeping information about users and various
actions in databases.
<a href="libc_29.html#User-Database">29.13 User Database</a> Functions and data structures for
accessing the user database.
<a href="libc_29.html#Group-Database">29.14 Group Database</a> Functions and data structures for
accessing the group database.
<a href="libc_29.html#Database-Example">29.15 User and Group Database Example</a> Example program showing the use of database
inquiry functions.
<a href="libc_29.html#Netgroup-Database">29.16 Netgroup Database</a> Functions for accessing the netgroup database.
<p><em>User Accounting Database
</em></p>
<a href="libc_29.html#Manipulating-the-Database">29.12.1 Manipulating the User Accounting Database</a> Scanning and modifying the user
accounting database.
<a href="libc_29.html#XPG-Functions">29.12.2 XPG User Accounting Database Functions</a> A standardized way for doing the same thing.
<a href="libc_29.html#Logging-In-and-Out">29.12.3 Logging In and Out</a> Functions from BSD that modify the user
accounting database.
<p><em>User Database
</em></p>
<a href="libc_29.html#User-Data-Structure">29.13.1 The Data Structure that Describes a User</a> What each user record contains.
<a href="libc_29.html#Lookup-User">29.13.2 Looking Up One User</a> How to look for a particular user.
<a href="libc_29.html#Scanning-All-Users">29.13.3 Scanning the List of All Users</a> Scanning the list of all users, one by one.
<a href="libc_29.html#Writing-a-User-Entry">29.13.4 Writing a User Entry</a> How a program can rewrite a user’s record.
<p><em>Group Database
</em></p>
<a href="libc_29.html#Group-Data-Structure">29.14.1 The Data Structure for a Group</a> What each group record contains.
<a href="libc_29.html#Lookup-Group">29.14.2 Looking Up One Group</a> How to look for a particular group.
<a href="libc_29.html#Scanning-All-Groups">29.14.3 Scanning the List of All Groups</a> Scanning the list of all groups.
<p><em>Netgroup Database
</em></p>
<a href="libc_29.html#Netgroup-Data">29.16.1 Netgroup Data</a> Data in the Netgroup database and where
it comes from.
<a href="libc_29.html#Lookup-Netgroup">29.16.2 Looking up one Netgroup</a> How to look for a particular netgroup.
<a href="libc_29.html#Netgroup-Membership">29.16.3 Testing for Netgroup Membership</a> How to test for netgroup membership.
<p><em>System Management
</em></p>
<a href="libc_30.html#Host-Identification">30.1 Host Identification</a> Determining the name of the machine.
<a href="libc_30.html#Platform-Type">30.2 Platform Type Identification</a> Determining operating system and basic
machine type
<a href="libc_30.html#Filesystem-Handling">30.3 Controlling and Querying Mounts</a> Controlling/querying mounts
<a href="libc_30.html#System-Parameters">30.4 System Parameters</a> Getting and setting various system parameters
<p><em>Filesystem Handling
</em></p>
<a href="libc_30.html#Mount-Information">30.3.1 Mount Information</a> What is or could be mounted?
<a href="libc_30.html#Mount_002dUnmount_002dRemount">30.3.2 Mount, Unmount, Remount</a> Controlling what is mounted and how
<p><em>Mount Information
</em></p>
<a href="libc_30.html#fstab">30.3.1.1 The ‘<tt>fstab</tt>’ file</a> The ‘<tt>fstab</tt>’ file
<a href="libc_30.html#mtab">30.3.1.2 The ‘<tt>mtab</tt>’ file</a> The ‘<tt>mtab</tt>’ file
<a href="libc_30.html#Other-Mount-Information">30.3.1.3 Other (Non-libc) Sources of Mount Information</a> Other (non-libc) sources of mount information
<p><em>System Configuration
</em></p>
<a href="libc_31.html#General-Limits">31.1 General Capacity Limits</a> Constants and functions that describe
various process-related limits that have
one uniform value for any given machine.
<a href="libc_31.html#System-Options">31.2 Overall System Options</a> Optional POSIX features.
<a href="libc_31.html#Version-Supported">31.3 Which Version of POSIX is Supported</a> Version numbers of POSIX.1 and POSIX.2.
<a href="libc_31.html#Sysconf">31.4 Using <code>sysconf</code></a> Getting specific configuration values
of general limits and system options.
<a href="libc_31.html#Minimums">31.5 Minimum Values for General Capacity Limits</a> Minimum values for general limits.
<a href="libc_31.html#Limits-for-Files">31.6 Limits on File System Capacity</a> Size limitations that pertain to individual files.
These can vary between file systems
or even from file to file.
<a href="libc_31.html#Options-for-Files">31.7 Optional Features in File Support</a> Optional features that some files may support.
<a href="libc_31.html#File-Minimums">31.8 Minimum Values for File System Limits</a> Minimum values for file limits.
<a href="libc_31.html#Pathconf">31.9 Using <code>pathconf</code></a> Getting the limit values for a particular file.
<a href="libc_31.html#Utility-Limits">31.10 Utility Program Capacity Limits</a> Capacity limits of some POSIX.2 utility programs.
<a href="libc_31.html#Utility-Minimums">31.11 Minimum Values for Utility Limits</a> Minimum allowable values of those limits.
<a href="libc_31.html#String-Parameters">31.12 String-Valued Parameters</a> Getting the default search path.
<p><em>Sysconf
</em></p>
<a href="libc_31.html#Sysconf-Definition">31.4.1 Definition of <code>sysconf</code></a> Detailed specifications of <code>sysconf</code>.
<a href="libc_31.html#Constants-for-Sysconf">31.4.2 Constants for <code>sysconf</code> Parameters</a> The list of parameters <code>sysconf</code> can read.
<a href="libc_31.html#Examples-of-Sysconf">31.4.3 Examples of <code>sysconf</code></a> How to use <code>sysconf</code> and the parameter
macros properly together.
<p><em>Cryptographic Functions
</em></p>
<a href="libc_32.html#Legal-Problems">32.1 Legal Problems</a> This software can get you locked up, or worse.
<a href="libc_32.html#getpass">32.2 Reading Passwords</a> Prompting the user for a password.
<a href="libc_32.html#crypt">32.3 Encrypting Passwords</a> A one-way function for passwords.
<a href="libc_32.html#DES-Encryption">32.4 DES Encryption</a> Routines for DES encryption.
<p><em>Debugging Support
</em></p>
<a href="libc_33.html#Backtraces">33.1 Backtraces</a> Obtaining and printing a back trace of the
current stack.
<p><em>Language Features
</em></p>
<a href="libc_34.html#Consistency-Checking">A.1 Explicitly Checking Internal Consistency</a> Using <code>assert</code> to abort if
something “impossible” happens.
<a href="libc_34.html#Variadic-Functions">A.2 Variadic Functions</a> Defining functions with varying numbers
of args.
<a href="libc_34.html#Null-Pointer-Constant">A.3 Null Pointer Constant</a> The macro <code>NULL</code>.
<a href="libc_34.html#Important-Data-Types">A.4 Important Data Types</a> Data types for object sizes.
<a href="libc_34.html#Data-Type-Measurements">A.5 Data Type Measurements</a> Parameters of data type representations.
<p><em>Variadic Functions
</em></p>
<a href="libc_34.html#Why-Variadic">A.2.1 Why Variadic Functions are Used</a> Reasons for making functions take
variable arguments.
<a href="libc_34.html#How-Variadic">A.2.2 How Variadic Functions are Defined and Used</a> How to define and call variadic functions.
<a href="libc_34.html#Variadic-Example">A.2.3 Example of a Variadic Function</a> A complete example.
<p><em>How Variadic
</em></p>
<a href="libc_34.html#Variadic-Prototypes">A.2.2.1 Syntax for Variable Arguments</a> How to make a prototype for a function
with variable arguments.
<a href="libc_34.html#Receiving-Arguments">A.2.2.2 Receiving the Argument Values</a> Steps you must follow to access the
optional argument values.
<a href="libc_34.html#How-Many-Arguments">A.2.2.3 How Many Arguments Were Supplied</a> How to decide whether there are more arguments.
<a href="libc_34.html#Calling-Variadics">A.2.2.4 Calling Variadic Functions</a> Things you need to know about calling
variable arguments functions.
<a href="libc_34.html#Argument-Macros">A.2.2.5 Argument Access Macros</a> Detailed specification of the macros
for accessing variable arguments.
<a href="libc_34.html#Old-Varargs">A.2.3.1 Old-Style Variadic Functions</a> The pre-ISO way of defining variadic functions.
<p><em>Data Type Measurements
</em></p>
<a href="libc_34.html#Width-of-Type">A.5.1 Computing the Width of an Integer Data Type</a> How many bits does an integer type hold?
<a href="libc_34.html#Range-of-Type">A.5.2 Range of an Integer Type</a> What are the largest and smallest values
that an integer type can hold?
<a href="libc_34.html#Floating-Type-Macros">A.5.3 Floating Type Macros</a> Parameters that measure the floating point types.
<a href="libc_34.html#Structure-Measurement">A.5.4 Structure Field Offset Measurement</a> Getting measurements on structure types.
<p><em>Floating Type Macros
</em></p>
<a href="libc_34.html#Floating-Point-Concepts">A.5.3.1 Floating Point Representation Concepts</a> Definitions of terminology.
<a href="libc_34.html#Floating-Point-Parameters">A.5.3.2 Floating Point Parameters</a> Details of specific macros.
<a href="libc_34.html#IEEE-Floating-Point">A.5.3.3 IEEE Floating Point</a> The measurements for one common
representation.
<p><em>Installation
</em></p>
<a href="libc_36.html#Configuring-and-compiling">C.1 Configuring and compiling GNU Libc</a> How to compile and test GNU libc.
<a href="libc_36.html#Running-make-install">C.2 Installing the C Library</a> How to install it once you’ve got it
compiled.
<a href="libc_36.html#Tools-for-Compilation">C.3 Recommended Tools for Compilation</a> You’ll need these first.
<a href="libc_36.html#Linux">C.4 Specific advice for GNU/Linux systems</a> Specific advice for GNU/Linux systems.
<a href="libc_36.html#Reporting-Bugs">C.5 Reporting Bugs</a> So they’ll get fixed.
<p><em>Maintenance
</em></p>
<a href="libc_37.html#Source-Layout">D.1 Adding New Functions</a> How to add new functions or header files
to the GNU C library.
<a href="libc_37.html#Porting">D.2 Porting the GNU C Library</a> How to port the GNU C library to
a new machine or operating system.
<p><em>Porting
</em></p>
<a href="libc_37.html#Hierarchy-Conventions">D.2.1 Layout of the ‘<tt>sysdeps</tt>’ Directory Hierarchy</a> The layout of the ‘<tt>sysdeps</tt>’ hierarchy.
<a href="libc_37.html#Porting-to-Unix">D.2.2 Porting the GNU C Library to Unix Systems</a> Porting the library to an average
Unix-like system.
@end menu
</em></table>
</table>
<a name="Introduction-1"></a>
<h1 class="chapter">1. Introduction</h1>
<p>The C language provides no built-in facilities for performing such
common operations as input/output, memory management, string
manipulation, and the like. Instead, these facilities are defined
in a standard <em>library</em>, which you compile and link with your
programs.
<a name="index-library"></a>
</p>
<p>The GNU C library, described in this document, defines all of the
library functions that are specified by the ISO C standard, as well as
additional features specific to POSIX and other derivatives of the Unix
operating system, and extensions specific to the GNU system.
</p>
<p>The purpose of this manual is to tell you how to use the facilities
of the GNU library. We have mentioned which features belong to which
standards to help you identify things that are potentially non-portable
to other systems. But the emphasis in this manual is not on strict
portability.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top"><a href="#Getting-Started">1.1 Getting Started</a></td><td> </td><td align="left" valign="top"> What this manual is for and how to use it.
</td></tr>
<tr><td align="left" valign="top"><a href="#Standards-and-Portability">1.2 Standards and Portability</a></td><td> </td><td align="left" valign="top"> Standards and sources upon which the GNU
C library is based.
</td></tr>
<tr><td align="left" valign="top"><a href="#Using-the-Library">1.3 Using the Library</a></td><td> </td><td align="left" valign="top"> Some practical uses for the library.
</td></tr>
<tr><td align="left" valign="top"><a href="#Roadmap-to-the-Manual">1.4 Roadmap to the Manual</a></td><td> </td><td align="left" valign="top"> Overview of the remaining chapters in
this manual.
</td></tr>
</table>
<hr size="6">
<a name="Getting-Started"></a>
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<tr><td valign="middle" align="left">[<a href="#Introduction" title="Previous section in reading order"> < </a>]</td>
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<td valign="middle" align="left">[<a href="libc_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
</tr></table>
<a name="Getting-Started-1"></a>
<h2 class="section">1.1 Getting Started</h2>
<p>This manual is written with the assumption that you are at least
somewhat familiar with the C programming language and basic programming
concepts. Specifically, familiarity with ISO standard C
(see section <a href="#ISO-C">ISO C</a>), rather than “traditional” pre-ISO C dialects, is
assumed.
</p>
<p>The GNU C library includes several <em>header files</em>, each of which
provides definitions and declarations for a group of related facilities;
this information is used by the C compiler when processing your program.
For example, the header file ‘<tt>stdio.h</tt>’ declares facilities for
performing input and output, and the header file ‘<tt>string.h</tt>’
declares string processing utilities. The organization of this manual
generally follows the same division as the header files.
</p>
<p>If you are reading this manual for the first time, you should read all
of the introductory material and skim the remaining chapters. There are
a <em>lot</em> of functions in the GNU C library and it’s not realistic to
expect that you will be able to remember exactly <em>how</em> to use each
and every one of them. It’s more important to become generally familiar
with the kinds of facilities that the library provides, so that when you
are writing your programs you can recognize <em>when</em> to make use of
library functions, and <em>where</em> in this manual you can find more
specific information about them.
</p>
<hr size="6">
<a name="Standards-and-Portability"></a>
<table cellpadding="1" cellspacing="1" border="0">
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</tr></table>
<a name="Standards-and-Portability-1"></a>
<h2 class="section">1.2 Standards and Portability</h2>
<a name="index-standards"></a>
<p>This section discusses the various standards and other sources that the
GNU C library is based upon. These sources include the ISO C and
POSIX standards, and the System V and Berkeley Unix implementations.
</p>
<p>The primary focus of this manual is to tell you how to make effective
use of the GNU library facilities. But if you are concerned about
making your programs compatible with these standards, or portable to
operating systems other than GNU, this can affect how you use the
library. This section gives you an overview of these standards, so that
you will know what they are when they are mentioned in other parts of
the manual.
</p>
<p>See section <a href="libc_35.html#Library-Summary">Summary of Library Facilities</a>, for an alphabetical list of the functions and
other symbols provided by the library. This list also states which
standards each function or symbol comes from.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top"><a href="#ISO-C">1.2.1 ISO C</a></td><td> </td><td align="left" valign="top"> The international standard for the C
programming language.
</td></tr>
<tr><td align="left" valign="top"><a href="#POSIX">1.2.2 POSIX (The Portable Operating System Interface)</a></td><td> </td><td align="left" valign="top"> The ISO/IEC 9945 (aka IEEE 1003) standards
for operating systems.
</td></tr>
<tr><td align="left" valign="top"><a href="#Berkeley-Unix">1.2.3 Berkeley Unix</a></td><td> </td><td align="left" valign="top"> BSD and SunOS.
</td></tr>
<tr><td align="left" valign="top"><a href="#SVID">1.2.4 SVID (The System V Interface Description)</a></td><td> </td><td align="left" valign="top"> The System V Interface Description.
</td></tr>
<tr><td align="left" valign="top"><a href="#XPG">1.2.5 XPG (The X/Open Portability Guide)</a></td><td> </td><td align="left" valign="top"> The X/Open Portability Guide.
</td></tr>
</table>
<hr size="6">
<a name="ISO-C"></a>
<table cellpadding="1" cellspacing="1" border="0">
<tr><td valign="middle" align="left">[<a href="#Standards-and-Portability" title="Previous section in reading order"> < </a>]</td>
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<td valign="middle" align="left">[<a href="libc_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
</tr></table>
<a name="ISO-C-1"></a>
<h3 class="subsection">1.2.1 ISO C</h3>
<a name="index-ISO-C"></a>
<p>The GNU C library is compatible with the C standard adopted by the
American National Standards Institute (ANSI):
<cite>American National Standard X3.159-1989—“ANSI C”</cite> and later
by the International Standardization Organization (ISO):
<cite>ISO/IEC 9899:1990, “Programming languages—C”</cite>.
We here refer to the standard as ISO C since this is the more
general standard in respect of ratification.
The header files and library facilities that make up the GNU library are
a superset of those specified by the ISO C standard.
</p>
<a name="index-gcc"></a>
<p>If you are concerned about strict adherence to the ISO C standard, you
should use the ‘<samp>-ansi</samp>’ option when you compile your programs with
the GNU C compiler. This tells the compiler to define <em>only</em> ISO
standard features from the library header files, unless you explicitly
ask for additional features. See section <a href="#Feature-Test-Macros">Feature Test Macros</a>, for
information on how to do this.
</p>
<p>Being able to restrict the library to include only ISO C features is
important because ISO C puts limitations on what names can be defined
by the library implementation, and the GNU extensions don’t fit these
limitations. See section <a href="#Reserved-Names">Reserved Names</a>, for more information about these
restrictions.
</p>
<p>This manual does not attempt to give you complete details on the
differences between ISO C and older dialects. It gives advice on how
to write programs to work portably under multiple C dialects, but does
not aim for completeness.
</p>
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<a name="POSIX-_0028The-Portable-Operating-System-Interface_0029"></a>
<h3 class="subsection">1.2.2 POSIX (The Portable Operating System Interface)</h3>
<a name="index-POSIX"></a>
<a name="index-POSIX_002e1"></a>
<a name="index-IEEE-Std-1003_002e1"></a>
<a name="index-ISO_002fIEC-9945_002d1"></a>
<a name="index-POSIX_002e2"></a>
<a name="index-IEEE-Std-1003_002e2"></a>
<a name="index-ISO_002fIEC-9945_002d2"></a>
<p>The GNU library is also compatible with the ISO <em>POSIX</em> family of
standards, known more formally as the <em>Portable Operating System
Interface for Computer Environments</em> (ISO/IEC 9945). They were also
published as ANSI/IEEE Std 1003. POSIX is derived mostly from various
versions of the Unix operating system.
</p>
<p>The library facilities specified by the POSIX standards are a superset
of those required by ISO C; POSIX specifies additional features for
ISO C functions, as well as specifying new additional functions. In
general, the additional requirements and functionality defined by the
POSIX standards are aimed at providing lower-level support for a
particular kind of operating system environment, rather than general
programming language support which can run in many diverse operating
system environments.
</p>
<p>The GNU C library implements all of the functions specified in
<cite>ISO/IEC 9945-1:1996, the POSIX System Application Program
Interface</cite>, commonly referred to as POSIX.1. The primary extensions to
the ISO C facilities specified by this standard include file system
interface primitives (see section <a href="libc_14.html#File-System-Interface">File System Interface</a>), device-specific
terminal control functions (see section <a href="libc_17.html#Low_002dLevel-Terminal-Interface">Low-Level Terminal Interface</a>), and
process control functions (see section <a href="libc_26.html#Processes">Processes</a>).
</p>
<p>Some facilities from <cite>ISO/IEC 9945-2:1993, the POSIX Shell and
Utilities standard</cite> (POSIX.2) are also implemented in the GNU library.
These include utilities for dealing with regular expressions and other
pattern matching facilities (see section <a href="libc_10.html#Pattern-Matching">Pattern Matching</a>).
</p>
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<a name="Berkeley-Unix-1"></a>
<h3 class="subsection">1.2.3 Berkeley Unix</h3>
<a name="index-BSD-Unix"></a>
<a name="index-4_002en-BSD-Unix"></a>
<a name="index-Berkeley-Unix"></a>
<a name="index-SunOS"></a>
<a name="index-Unix_002c-Berkeley"></a>
<p>The GNU C library defines facilities from some versions of Unix which
are not formally standardized, specifically from the 4.2 BSD, 4.3 BSD,
and 4.4 BSD Unix systems (also known as <em>Berkeley Unix</em>) and from
<em>SunOS</em> (a popular 4.2 BSD derivative that includes some Unix System
V functionality). These systems support most of the ISO C and POSIX
facilities, and 4.4 BSD and newer releases of SunOS in fact support them all.
</p>
<p>The BSD facilities include symbolic links (see section <a href="libc_14.html#Symbolic-Links">Symbolic Links</a>), the
<code>select</code> function (see section <a href="libc_13.html#Waiting-for-I_002fO">Waiting for Input or Output</a>), the BSD signal
functions (see section <a href="libc_24.html#BSD-Signal-Handling">BSD Signal Handling</a>), and sockets (see section <a href="libc_16.html#Sockets">Sockets</a>).
</p>
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<a name="SVID-_0028The-System-V-Interface-Description_0029"></a>
<h3 class="subsection">1.2.4 SVID (The System V Interface Description)</h3>
<a name="index-SVID"></a>
<a name="index-System-V-Unix"></a>
<a name="index-Unix_002c-System-V"></a>
<p>The <em>System V Interface Description</em> (SVID) is a document describing
the AT&T Unix System V operating system. It is to some extent a
superset of the POSIX standard (see section <a href="#POSIX">POSIX (The Portable Operating System Interface)</a>).
</p>
<p>The GNU C library defines most of the facilities required by the SVID
that are not also required by the ISO C or POSIX standards, for
compatibility with System V Unix and other Unix systems (such as
SunOS) which include these facilities. However, many of the more
obscure and less generally useful facilities required by the SVID are
not included. (In fact, Unix System V itself does not provide them all.)
</p>
<p>The supported facilities from System V include the methods for
inter-process communication and shared memory, the <code>hsearch</code> and
<code>drand48</code> families of functions, <code>fmtmsg</code> and several of the
mathematical functions.
</p>
<hr size="6">
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<a name="XPG-_0028The-X_002fOpen-Portability-Guide_0029"></a>
<h3 class="subsection">1.2.5 XPG (The X/Open Portability Guide)</h3>
<p>The X/Open Portability Guide, published by the X/Open Company, Ltd., is
a more general standard than POSIX. X/Open owns the Unix copyright and
the XPG specifies the requirements for systems which are intended to be
a Unix system.
</p>
<p>The GNU C library complies to the X/Open Portability Guide, Issue 4.2,
with all extensions common to XSI (X/Open System Interface)
compliant systems and also all X/Open UNIX extensions.
</p>
<p>The additions on top of POSIX are mainly derived from functionality
available in System V and BSD systems. Some of the really bad
mistakes in System V systems were corrected, though. Since
fulfilling the XPG standard with the Unix extensions is a
precondition for getting the Unix brand chances are good that the
functionality is available on commercial systems.
</p>
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<a name="Using-the-Library-1"></a>
<h2 class="section">1.3 Using the Library</h2>
<p>This section describes some of the practical issues involved in using
the GNU C library.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top"><a href="#Header-Files">1.3.1 Header Files</a></td><td> </td><td align="left" valign="top"> How to include the header files in your
programs.
</td></tr>
<tr><td align="left" valign="top"><a href="#Macro-Definitions">1.3.2 Macro Definitions of Functions</a></td><td> </td><td align="left" valign="top"> Some functions in the library may really
be implemented as macros.
</td></tr>
<tr><td align="left" valign="top"><a href="#Reserved-Names">1.3.3 Reserved Names</a></td><td> </td><td align="left" valign="top"> The C standard reserves some names for
the library, and some for users.
</td></tr>
<tr><td align="left" valign="top"><a href="#Feature-Test-Macros">1.3.4 Feature Test Macros</a></td><td> </td><td align="left" valign="top"> How to control what names are defined.
</td></tr>
</table>
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<a name="Header-Files-1"></a>
<h3 class="subsection">1.3.1 Header Files</h3>
<a name="index-header-files"></a>
<p>Libraries for use by C programs really consist of two parts: <em>header
files</em> that define types and macros and declare variables and
functions; and the actual library or <em>archive</em> that contains the
definitions of the variables and functions.
</p>
<p>(Recall that in C, a <em>declaration</em> merely provides information that
a function or variable exists and gives its type. For a function
declaration, information about the types of its arguments might be
provided as well. The purpose of declarations is to allow the compiler
to correctly process references to the declared variables and functions.
A <em>definition</em>, on the other hand, actually allocates storage for a
variable or says what a function does.)
<a name="index-definition-_0028compared-to-declaration_0029"></a>
<a name="index-declaration-_0028compared-to-definition_0029"></a>
</p>
<p>In order to use the facilities in the GNU C library, you should be sure
that your program source files include the appropriate header files.
This is so that the compiler has declarations of these facilities
available and can correctly process references to them. Once your
program has been compiled, the linker resolves these references to
the actual definitions provided in the archive file.
</p>
<p>Header files are included into a program source file by the
‘<samp>#include</samp>’ preprocessor directive. The C language supports two
forms of this directive; the first,
</p>
<table><tr><td> </td><td><pre class="smallexample">#include "<var>header</var>"
</pre></td></tr></table>
<p>is typically used to include a header file <var>header</var> that you write
yourself; this would contain definitions and declarations describing the
interfaces between the different parts of your particular application.
By contrast,
</p>
<table><tr><td> </td><td><pre class="smallexample">#include <file.h>
</pre></td></tr></table>
<p>is typically used to include a header file ‘<tt>file.h</tt>’ that contains
definitions and declarations for a standard library. This file would
normally be installed in a standard place by your system administrator.
You should use this second form for the C library header files.
</p>
<p>Typically, ‘<samp>#include</samp>’ directives are placed at the top of the C
source file, before any other code. If you begin your source files with
some comments explaining what the code in the file does (a good idea),
put the ‘<samp>#include</samp>’ directives immediately afterwards, following the
feature test macro definition (see section <a href="#Feature-Test-Macros">Feature Test Macros</a>).
</p>
<p>For more information about the use of header files and ‘<samp>#include</samp>’
directives, see <a href="../cpp/Header-Files.html#Header-Files">(cpp.info)Header Files</a> section ‘Header Files’ in <cite>The GNU C Preprocessor Manual</cite>.
</p>
<p>The GNU C library provides several header files, each of which contains
the type and macro definitions and variable and function declarations
for a group of related facilities. This means that your programs may
need to include several header files, depending on exactly which
facilities you are using.
</p>
<p>Some library header files include other library header files
automatically. However, as a matter of programming style, you should
not rely on this; it is better to explicitly include all the header
files required for the library facilities you are using. The GNU C
library header files have been written in such a way that it doesn’t
matter if a header file is accidentally included more than once;
including a header file a second time has no effect. Likewise, if your
program needs to include multiple header files, the order in which they
are included doesn’t matter.
</p>
<p><strong>Compatibility Note:</strong> Inclusion of standard header files in any
order and any number of times works in any ISO C implementation.
However, this has traditionally not been the case in many older C
implementations.
</p>
<p>Strictly speaking, you don’t <em>have to</em> include a header file to use
a function it declares; you could declare the function explicitly
yourself, according to the specifications in this manual. But it is
usually better to include the header file because it may define types
and macros that are not otherwise available and because it may define
more efficient macro replacements for some functions. It is also a sure
way to have the correct declaration.
</p>
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<a name="Macro-Definitions-of-Functions"></a>
<h3 class="subsection">1.3.2 Macro Definitions of Functions</h3>
<a name="index-shadowing-functions-with-macros"></a>
<a name="index-removing-macros-that-shadow-functions"></a>
<a name="index-undefining-macros-that-shadow-functions"></a>
<p>If we describe something as a function in this manual, it may have a
macro definition as well. This normally has no effect on how your
program runs—the macro definition does the same thing as the function
would. In particular, macro equivalents for library functions evaluate
arguments exactly once, in the same way that a function call would. The
main reason for these macro definitions is that sometimes they can
produce an inline expansion that is considerably faster than an actual
function call.
</p>
<p>Taking the address of a library function works even if it is also
defined as a macro. This is because, in this context, the name of the
function isn’t followed by the left parenthesis that is syntactically
necessary to recognize a macro call.
</p>
<p>You might occasionally want to avoid using the macro definition of a
function—perhaps to make your program easier to debug. There are
two ways you can do this:
</p>
<ul>
<li>
You can avoid a macro definition in a specific use by enclosing the name
of the function in parentheses. This works because the name of the
function doesn’t appear in a syntactic context where it is recognizable
as a macro call.
</li><li>
You can suppress any macro definition for a whole source file by using
the ‘<samp>#undef</samp>’ preprocessor directive, unless otherwise stated
explicitly in the description of that facility.
</li></ul>
<p>For example, suppose the header file ‘<tt>stdlib.h</tt>’ declares a function
named <code>abs</code> with
</p>
<table><tr><td> </td><td><pre class="smallexample">extern int abs (int);
</pre></td></tr></table>
<p>and also provides a macro definition for <code>abs</code>. Then, in:
</p>
<table><tr><td> </td><td><pre class="smallexample">#include <stdlib.h>
int f (int *i) { return abs (++*i); }
</pre></td></tr></table>
<p>the reference to <code>abs</code> might refer to either a macro or a function.
On the other hand, in each of the following examples the reference is
to a function and not a macro.
</p>
<table><tr><td> </td><td><pre class="smallexample">#include <stdlib.h>
int g (int *i) { return (abs) (++*i); }
#undef abs
int h (int *i) { return abs (++*i); }
</pre></td></tr></table>
<p>Since macro definitions that double for a function behave in
exactly the same way as the actual function version, there is usually no
need for any of these methods. In fact, removing macro definitions usually
just makes your program slower.
</p>
<hr size="6">
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<a name="Reserved-Names-1"></a>
<h3 class="subsection">1.3.3 Reserved Names</h3>
<a name="index-reserved-names"></a>
<a name="index-name-space"></a>
<p>The names of all library types, macros, variables and functions that
come from the ISO C standard are reserved unconditionally; your program
<strong>may not</strong> redefine these names. All other library names are
reserved if your program explicitly includes the header file that
defines or declares them. There are several reasons for these
restrictions:
</p>
<ul>
<li>
Other people reading your code could get very confused if you were using
a function named <code>exit</code> to do something completely different from
what the standard <code>exit</code> function does, for example. Preventing
this situation helps to make your programs easier to understand and
contributes to modularity and maintainability.
</li><li>
It avoids the possibility of a user accidentally redefining a library
function that is called by other library functions. If redefinition
were allowed, those other functions would not work properly.
</li><li>
It allows the compiler to do whatever special optimizations it pleases
on calls to these functions, without the possibility that they may have
been redefined by the user. Some library facilities, such as those for
dealing with variadic arguments (see section <a href="libc_34.html#Variadic-Functions">Variadic Functions</a>)
and non-local exits (see section <a href="libc_23.html#Non_002dLocal-Exits">Non-Local Exits</a>), actually require a
considerable amount of cooperation on the part of the C compiler, and
with respect to the implementation, it might be easier for the compiler
to treat these as built-in parts of the language.
</li></ul>
<p>In addition to the names documented in this manual, reserved names
include all external identifiers (global functions and variables) that
begin with an underscore (‘<samp>_</samp>’) and all identifiers regardless of
use that begin with either two underscores or an underscore followed by
a capital letter are reserved names. This is so that the library and
header files can define functions, variables, and macros for internal
purposes without risk of conflict with names in user programs.
</p>
<p>Some additional classes of identifier names are reserved for future
extensions to the C language or the POSIX.1 environment. While using these
names for your own purposes right now might not cause a problem, they do
raise the possibility of conflict with future versions of the C
or POSIX standards, so you should avoid these names.
</p>
<ul>
<li>
Names beginning with a capital ‘<samp>E</samp>’ followed a digit or uppercase
letter may be used for additional error code names. See section <a href="libc_2.html#Error-Reporting">Error Reporting</a>.
</li><li>
Names that begin with either ‘<samp>is</samp>’ or ‘<samp>to</samp>’ followed by a
lowercase letter may be used for additional character testing and
conversion functions. See section <a href="libc_4.html#Character-Handling">Character Handling</a>.
</li><li>
Names that begin with ‘<samp>LC_</samp>’ followed by an uppercase letter may be
used for additional macros specifying locale attributes.
See section <a href="libc_7.html#Locales">Locales and Internationalization</a>.
</li><li>
Names of all existing mathematics functions (see section <a href="libc_19.html#Mathematics">Mathematics</a>)
suffixed with ‘<samp>f</samp>’ or ‘<samp>l</samp>’ are reserved for corresponding
functions that operate on <code>float</code> and <code>long double</code> arguments,
respectively.
</li><li>
Names that begin with ‘<samp>SIG</samp>’ followed by an uppercase letter are
reserved for additional signal names. See section <a href="libc_24.html#Standard-Signals">Standard Signals</a>.
</li><li>
Names that begin with ‘<samp>SIG_</samp>’ followed by an uppercase letter are
reserved for additional signal actions. See section <a href="libc_24.html#Basic-Signal-Handling">Basic Signal Handling</a>.
</li><li>
Names beginning with ‘<samp>str</samp>’, ‘<samp>mem</samp>’, or ‘<samp>wcs</samp>’ followed by a
lowercase letter are reserved for additional string and array functions.
See section <a href="libc_5.html#String-and-Array-Utilities">String and Array Utilities</a>.
</li><li>
Names that end with ‘<samp>_t</samp>’ are reserved for additional type names.
</li></ul>
<p>In addition, some individual header files reserve names beyond
those that they actually define. You only need to worry about these
restrictions if your program includes that particular header file.
</p>
<ul>
<li>
The header file ‘<tt>dirent.h</tt>’ reserves names prefixed with
‘<samp>d_</samp>’.
<a name="index-dirent_002eh"></a>
</li><li>
The header file ‘<tt>fcntl.h</tt>’ reserves names prefixed with
‘<samp>l_</samp>’, ‘<samp>F_</samp>’, ‘<samp>O_</samp>’, and ‘<samp>S_</samp>’.
<a name="index-fcntl_002eh"></a>
</li><li>
The header file ‘<tt>grp.h</tt>’ reserves names prefixed with ‘<samp>gr_</samp>’.
<a name="index-grp_002eh"></a>
</li><li>
The header file ‘<tt>limits.h</tt>’ reserves names suffixed with ‘<samp>_MAX</samp>’.
<a name="index-limits_002eh"></a>
</li><li>
The header file ‘<tt>pwd.h</tt>’ reserves names prefixed with ‘<samp>pw_</samp>’.
<a name="index-pwd_002eh"></a>
</li><li>
The header file ‘<tt>signal.h</tt>’ reserves names prefixed with ‘<samp>sa_</samp>’
and ‘<samp>SA_</samp>’.
<a name="index-signal_002eh"></a>
</li><li>
The header file ‘<tt>sys/stat.h</tt>’ reserves names prefixed with ‘<samp>st_</samp>’
and ‘<samp>S_</samp>’.
<a name="index-sys_002fstat_002eh"></a>
</li><li>
The header file ‘<tt>sys/times.h</tt>’ reserves names prefixed with ‘<samp>tms_</samp>’.
<a name="index-sys_002ftimes_002eh"></a>
</li><li>
The header file ‘<tt>termios.h</tt>’ reserves names prefixed with ‘<samp>c_</samp>’,
‘<samp>V</samp>’, ‘<samp>I</samp>’, ‘<samp>O</samp>’, and ‘<samp>TC</samp>’; and names prefixed with
‘<samp>B</samp>’ followed by a digit.
<a name="index-termios_002eh"></a>
</li></ul>
<hr size="6">
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<a name="Feature-Test-Macros-1"></a>
<h3 class="subsection">1.3.4 Feature Test Macros</h3>
<a name="index-feature-test-macros"></a>
<p>The exact set of features available when you compile a source file
is controlled by which <em>feature test macros</em> you define.
</p>
<p>If you compile your programs using ‘<samp>gcc -ansi</samp>’, you get only the
ISO C library features, unless you explicitly request additional
features by defining one or more of the feature macros.
See <a href="../gcc/Invoking-GCC.html#Invoking-GCC">(gcc.info)Invoking GCC</a> section ‘GNU CC Command Options’ in <cite>The GNU CC Manual</cite>,
for more information about GCC options.
</p>
<p>You should define these macros by using ‘<samp>#define</samp>’ preprocessor
directives at the top of your source code files. These directives
<em>must</em> come before any <code>#include</code> of a system header file. It
is best to make them the very first thing in the file, preceded only by
comments. You could also use the ‘<samp>-D</samp>’ option to GCC, but it’s
better if you make the source files indicate their own meaning in a
self-contained way.
</p>
<p>This system exists to allow the library to conform to multiple standards.
Although the different standards are often described as supersets of each
other, they are usually incompatible because larger standards require
functions with names that smaller ones reserve to the user program. This
is not mere pedantry — it has been a problem in practice. For instance,
some non-GNU programs define functions named <code>getline</code> that have
nothing to do with this library’s <code>getline</code>. They would not be
compilable if all features were enabled indiscriminately.
</p>
<p>This should not be used to verify that a program conforms to a limited
standard. It is insufficient for this purpose, as it will not protect you
from including header files outside the standard, or relying on semantics
undefined within the standard.
</p>
<dl>
<dt><a name="index-_005fPOSIX_005fSOURCE"></a><u>Macro:</u> <b>_POSIX_SOURCE</b></dt>
<dd><p>If you define this macro, then the functionality from the POSIX.1
standard (IEEE Standard 1003.1) is available, as well as all of the
ISO C facilities.
</p>
<p>The state of <code>_POSIX_SOURCE</code> is irrelevant if you define the
macro <code>_POSIX_C_SOURCE</code> to a positive integer.
</p></dd></dl>
<dl>
<dt><a name="index-_005fPOSIX_005fC_005fSOURCE"></a><u>Macro:</u> <b>_POSIX_C_SOURCE</b></dt>
<dd><p>Define this macro to a positive integer to control which POSIX
functionality is made available. The greater the value of this macro,
the more functionality is made available.
</p>
<p>If you define this macro to a value greater than or equal to <code>1</code>,
then the functionality from the 1990 edition of the POSIX.1 standard
(IEEE Standard 1003.1-1990) is made available.
</p>
<p>If you define this macro to a value greater than or equal to <code>2</code>,
then the functionality from the 1992 edition of the POSIX.2 standard
(IEEE Standard 1003.2-1992) is made available.
</p>
<p>If you define this macro to a value greater than or equal to <code>199309L</code>,
then the functionality from the 1993 edition of the POSIX.1b standard
(IEEE Standard 1003.1b-1993) is made available.
</p>
<p>Greater values for <code>_POSIX_C_SOURCE</code> will enable future extensions.
The POSIX standards process will define these values as necessary, and
the GNU C Library should support them some time after they become standardized.
The 1996 edition of POSIX.1 (ISO/IEC 9945-1: 1996) states that
if you define <code>_POSIX_C_SOURCE</code> to a value greater than
or equal to <code>199506L</code>, then the functionality from the 1996
edition is made available.
</p></dd></dl>
<dl>
<dt><a name="index-_005fBSD_005fSOURCE"></a><u>Macro:</u> <b>_BSD_SOURCE</b></dt>
<dd><p>If you define this macro, functionality derived from 4.3 BSD Unix is
included as well as the ISO C, POSIX.1, and POSIX.2 material.
</p>
<p>Some of the features derived from 4.3 BSD Unix conflict with the
corresponding features specified by the POSIX.1 standard. If this
macro is defined, the 4.3 BSD definitions take precedence over the
POSIX definitions.
</p>
<p>Due to the nature of some of the conflicts between 4.3 BSD and POSIX.1,
you need to use a special <em>BSD compatibility library</em> when linking
programs compiled for BSD compatibility. This is because some functions
must be defined in two different ways, one of them in the normal C
library, and one of them in the compatibility library. If your program
defines <code>_BSD_SOURCE</code>, you must give the option ‘<samp>-lbsd-compat</samp>’
to the compiler or linker when linking the program, to tell it to find
functions in this special compatibility library before looking for them in
the normal C library.
<a name="index-_002dlbsd_002dcompat"></a>
<a name="index-bsd_002dcompat"></a>
<a name="index-BSD-compatibility-library_002e"></a>
</p></dd></dl>
<dl>
<dt><a name="index-_005fSVID_005fSOURCE"></a><u>Macro:</u> <b>_SVID_SOURCE</b></dt>
<dd><p>If you define this macro, functionality derived from SVID is
included as well as the ISO C, POSIX.1, POSIX.2, and X/Open material.
</p></dd></dl>
<dl>
<dt><a name="index-_005fXOPEN_005fSOURCE"></a><u>Macro:</u> <b>_XOPEN_SOURCE</b></dt>
<dt><a name="index-_005fXOPEN_005fSOURCE_005fEXTENDED"></a><u>Macro:</u> <b>_XOPEN_SOURCE_EXTENDED</b></dt>
<dd><p>If you define this macro, functionality described in the X/Open
Portability Guide is included. This is a superset of the POSIX.1 and
POSIX.2 functionality and in fact <code>_POSIX_SOURCE</code> and
<code>_POSIX_C_SOURCE</code> are automatically defined.
</p>
<p>As the unification of all Unices, functionality only available in
BSD and SVID is also included.
</p>
<p>If the macro <code>_XOPEN_SOURCE_EXTENDED</code> is also defined, even more
functionality is available. The extra functions will make all functions
available which are necessary for the X/Open Unix brand.
</p>
<p>If the macro <code>_XOPEN_SOURCE</code> has the value <em>500</em> this includes
all functionality described so far plus some new definitions from the
Single Unix Specification, version 2.
</p></dd></dl>
<dl>
<dt><a name="index-_005fLARGEFILE_005fSOURCE"></a><u>Macro:</u> <b>_LARGEFILE_SOURCE</b></dt>
<dd><p>If this macro is defined some extra functions are available which
rectify a few shortcomings in all previous standards. Specifically,
the functions <code>fseeko</code> and <code>ftello</code> are available. Without
these functions the difference between the ISO C interface
(<code>fseek</code>, <code>ftell</code>) and the low-level POSIX interface
(<code>lseek</code>) would lead to problems.
</p>
<p>This macro was introduced as part of the Large File Support extension (LFS).
</p></dd></dl>
<dl>
<dt><a name="index-_005fLARGEFILE64_005fSOURCE"></a><u>Macro:</u> <b>_LARGEFILE64_SOURCE</b></dt>
<dd><p>If you define this macro an additional set of functions is made available
which enables 32 bit systems to use files of sizes beyond
the usual limit of 2GB. This interface is not available if the system
does not support files that large. On systems where the natural file
size limit is greater than 2GB (i.e., on 64 bit systems) the new
functions are identical to the replaced functions.
</p>
<p>The new functionality is made available by a new set of types and
functions which replace the existing ones. The names of these new objects
contain <code>64</code> to indicate the intention, e.g., <code>off_t</code>
vs. <code>off64_t</code> and <code>fseeko</code> vs. <code>fseeko64</code>.
</p>
<p>This macro was introduced as part of the Large File Support extension
(LFS). It is a transition interface for the period when 64 bit
offsets are not generally used (see <code>_FILE_OFFSET_BITS</code>).
</p></dd></dl>
<dl>
<dt><a name="index-_005fFILE_005fOFFSET_005fBITS"></a><u>Macro:</u> <b>_FILE_OFFSET_BITS</b></dt>
<dd><p>This macro determines which file system interface shall be used, one
replacing the other. Whereas <code>_LARGEFILE64_SOURCE</code> makes the 64
bit interface available as an additional interface,
<code>_FILE_OFFSET_BITS</code> allows the 64 bit interface to
replace the old interface.
</p>
<p>If <code>_FILE_OFFSET_BITS</code> is undefined, or if it is defined to the
value <code>32</code>, nothing changes. The 32 bit interface is used and
types like <code>off_t</code> have a size of 32 bits on 32 bit
systems.
</p>
<p>If the macro is defined to the value <code>64</code>, the large file interface
replaces the old interface. I.e., the functions are not made available
under different names (as they are with <code>_LARGEFILE64_SOURCE</code>).
Instead the old function names now reference the new functions, e.g., a
call to <code>fseeko</code> now indeed calls <code>fseeko64</code>.
</p>
<p>This macro should only be selected if the system provides mechanisms for
handling large files. On 64 bit systems this macro has no effect
since the <code>*64</code> functions are identical to the normal functions.
</p>
<p>This macro was introduced as part of the Large File Support extension
(LFS).
</p></dd></dl>
<dl>
<dt><a name="index-_005fISOC99_005fSOURCE"></a><u>Macro:</u> <b>_ISOC99_SOURCE</b></dt>
<dd><p>Until the revised ISO C standard is widely adopted the new features
are not automatically enabled. The GNU libc nevertheless has a complete
implementation of the new standard and to enable the new features the
macro <code>_ISOC99_SOURCE</code> should be defined.
</p></dd></dl>
<dl>
<dt><a name="index-_005fGNU_005fSOURCE"></a><u>Macro:</u> <b>_GNU_SOURCE</b></dt>
<dd><p>If you define this macro, everything is included: ISO C89, ISO
C99, POSIX.1, POSIX.2, BSD, SVID, X/Open, LFS, and GNU extensions. In
the cases where POSIX.1 conflicts with BSD, the POSIX definitions take
precedence.
</p>
<p>If you want to get the full effect of <code>_GNU_SOURCE</code> but make the
BSD definitions take precedence over the POSIX definitions, use this
sequence of definitions:
</p>
<table><tr><td> </td><td><pre class="smallexample">#define _GNU_SOURCE
#define _BSD_SOURCE
#define _SVID_SOURCE
</pre></td></tr></table>
<p>Note that if you do this, you must link your program with the BSD
compatibility library by passing the ‘<samp>-lbsd-compat</samp>’ option to the
compiler or linker. <strong>NB:</strong> If you forget to do this, you may
get very strange errors at run time.
</p></dd></dl>
<dl>
<dt><a name="index-_005fREENTRANT"></a><u>Macro:</u> <b>_REENTRANT</b></dt>
<dt><a name="index-_005fTHREAD_005fSAFE"></a><u>Macro:</u> <b>_THREAD_SAFE</b></dt>
<dd><p>If you define one of these macros, reentrant versions of several functions get
declared. Some of the functions are specified in POSIX.1c but many others
are only available on a few other systems or are unique to GNU libc.
The problem is the delay in the standardization of the thread safe C library
interface.
</p>
<p>Unlike on some other systems, no special version of the C library must be
used for linking. There is only one version but while compiling this
it must have been specified to compile as thread safe.
</p></dd></dl>
<p>We recommend you use <code>_GNU_SOURCE</code> in new programs. If you don’t
specify the ‘<samp>-ansi</samp>’ option to GCC and don’t define any of these
macros explicitly, the effect is the same as defining
<code>_POSIX_C_SOURCE</code> to 2 and <code>_POSIX_SOURCE</code>,
<code>_SVID_SOURCE</code>, and <code>_BSD_SOURCE</code> to 1.
</p>
<p>When you define a feature test macro to request a larger class of features,
it is harmless to define in addition a feature test macro for a subset of
those features. For example, if you define <code>_POSIX_C_SOURCE</code>, then
defining <code>_POSIX_SOURCE</code> as well has no effect. Likewise, if you
define <code>_GNU_SOURCE</code>, then defining either <code>_POSIX_SOURCE</code> or
<code>_POSIX_C_SOURCE</code> or <code>_SVID_SOURCE</code> as well has no effect.
</p>
<p>Note, however, that the features of <code>_BSD_SOURCE</code> are not a subset of
any of the other feature test macros supported. This is because it defines
BSD features that take precedence over the POSIX features that are
requested by the other macros. For this reason, defining
<code>_BSD_SOURCE</code> in addition to the other feature test macros does have
an effect: it causes the BSD features to take priority over the conflicting
POSIX features.
</p>
<hr size="6">
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<a name="Roadmap-to-the-Manual-1"></a>
<h2 class="section">1.4 Roadmap to the Manual</h2>
<p>Here is an overview of the contents of the remaining chapters of
this manual.
</p>
<ul>
<li>
<a href="libc_2.html#Error-Reporting">Error Reporting</a>, describes how errors detected by the library
are reported.
</li><li>
<a href="libc_34.html#Language-Features">C Language Facilities in the Library</a>, contains information about library support for
standard parts of the C language, including things like the <code>sizeof</code>
operator and the symbolic constant <code>NULL</code>, how to write functions
accepting variable numbers of arguments, and constants describing the
ranges and other properties of the numerical types. There is also a simple
debugging mechanism which allows you to put assertions in your code, and
have diagnostic messages printed if the tests fail.
</li><li>
<a href="libc_3.html#Memory">Virtual Memory Allocation And Paging</a>, describes the GNU library’s facilities for managing and
using virtual and real memory, including dynamic allocation of virtual
memory. If you do not know in advance how much memory your program
needs, you can allocate it dynamically instead, and manipulate it via
pointers.
</li><li>
<a href="libc_4.html#Character-Handling">Character Handling</a>, contains information about character
classification functions (such as <code>isspace</code>) and functions for
performing case conversion.
</li><li>
<a href="libc_5.html#String-and-Array-Utilities">String and Array Utilities</a>, has descriptions of functions for
manipulating strings (null-terminated character arrays) and general
byte arrays, including operations such as copying and comparison.
</li><li>
<a href="libc_11.html#I_002fO-Overview">Input/Output Overview</a>, gives an overall look at the input and output
facilities in the library, and contains information about basic concepts
such as file names.
</li><li>
<a href="libc_12.html#I_002fO-on-Streams">Input/Output on Streams</a>, describes I/O operations involving streams (or
<code>FILE *</code> objects). These are the normal C library functions
from ‘<tt>stdio.h</tt>’.
</li><li>
<a href="libc_13.html#Low_002dLevel-I_002fO">Low-Level Input/Output</a>, contains information about I/O operations
on file descriptors. File descriptors are a lower-level mechanism
specific to the Unix family of operating systems.
</li><li>
<a href="libc_14.html#File-System-Interface">File System Interface</a>, has descriptions of operations on entire
files, such as functions for deleting and renaming them and for creating
new directories. This chapter also contains information about how you
can access the attributes of a file, such as its owner and file protection
modes.
</li><li>
<a href="libc_15.html#Pipes-and-FIFOs">Pipes and FIFOs</a>, contains information about simple interprocess
communication mechanisms. Pipes allow communication between two related
processes (such as between a parent and child), while FIFOs allow
communication between processes sharing a common file system on the same
machine.
</li><li>
<a href="libc_16.html#Sockets">Sockets</a>, describes a more complicated interprocess communication
mechanism that allows processes running on different machines to
communicate over a network. This chapter also contains information about
Internet host addressing and how to use the system network databases.
</li><li>
<a href="libc_17.html#Low_002dLevel-Terminal-Interface">Low-Level Terminal Interface</a>, describes how you can change the
attributes of a terminal device. If you want to disable echo of
characters typed by the user, for example, read this chapter.
</li><li>
<a href="libc_19.html#Mathematics">Mathematics</a>, contains information about the math library
functions. These include things like random-number generators and
remainder functions on integers as well as the usual trigonometric and
exponential functions on floating-point numbers.
</li><li>
<a href="libc_20.html#Arithmetic">Low-Level Arithmetic Functions</a>, describes functions
for simple arithmetic, analysis of floating-point values, and reading
numbers from strings.
</li><li>
<a href="libc_9.html#Searching-and-Sorting">Searching and Sorting</a>, contains information about functions
for searching and sorting arrays. You can use these functions on any
kind of array by providing an appropriate comparison function.
</li><li>
<a href="libc_10.html#Pattern-Matching">Pattern Matching</a>, presents functions for matching regular expressions
and shell file name patterns, and for expanding words as the shell does.
</li><li>
<a href="libc_21.html#Date-and-Time">Date and Time</a>, describes functions for measuring both calendar time
and CPU time, as well as functions for setting alarms and timers.
</li><li>
<a href="libc_6.html#Character-Set-Handling">Character Set Handling</a>, contains information about manipulating
characters and strings using character sets larger than will fit in
the usual <code>char</code> data type.
</li><li>
<a href="libc_7.html#Locales">Locales and Internationalization</a>, describes how selecting a particular country
or language affects the behavior of the library. For example, the locale
affects collation sequences for strings and how monetary values are
formatted.
</li><li>
<a href="libc_23.html#Non_002dLocal-Exits">Non-Local Exits</a>, contains descriptions of the <code>setjmp</code> and
<code>longjmp</code> functions. These functions provide a facility for
<code>goto</code>-like jumps which can jump from one function to another.
</li><li>
<a href="libc_24.html#Signal-Handling">Signal Handling</a>, tells you all about signals—what they are,
how to establish a handler that is called when a particular kind of
signal is delivered, and how to prevent signals from arriving during
critical sections of your program.
</li><li>
<a href="libc_25.html#Program-Basics">The Basic Program/System Interface</a>, tells how your programs can access their
command-line arguments and environment variables.
</li><li>
<a href="libc_26.html#Processes">Processes</a>, contains information about how to start new processes
and run programs.
</li><li>
<a href="libc_27.html#Job-Control">Job Control</a>, describes functions for manipulating process groups
and the controlling terminal. This material is probably only of
interest if you are writing a shell or other program which handles job
control specially.
</li><li>
<a href="libc_28.html#Name-Service-Switch">System Databases and Name Service Switch</a>, describes the services which are available
for looking up names in the system databases, how to determine which
service is used for which database, and how these services are
implemented so that contributors can design their own services.
</li><li>
<a href="libc_29.html#User-Database">User Database</a>, and <a href="libc_29.html#Group-Database">Group Database</a>, tell you how to access
the system user and group databases.
</li><li>
<a href="libc_30.html#System-Management">System Management</a>, describes functions for controlling and getting
information about the hardware and software configuration your program
is executing under.
</li><li>
<a href="libc_31.html#System-Configuration">System Configuration Parameters</a>, tells you how you can get information about
various operating system limits. Most of these parameters are provided for
compatibility with POSIX.
</li><li>
<a href="libc_35.html#Library-Summary">Summary of Library Facilities</a>, gives a summary of all the functions, variables, and
macros in the library, with complete data types and function prototypes,
and says what standard or system each is derived from.
</li><li>
<a href="libc_36.html#Installation">Installing the GNU C Library</a>, explains how to build and install the GNU C library on
your system, and how to report any bugs you might find.
</li><li>
<a href="libc_37.html#Maintenance">Library Maintenance</a>, explains how to add new functions or port the
library to a new system.
</li></ul>
<p>If you already know the name of the facility you are interested in, you
can look it up in <a href="libc_35.html#Library-Summary">Summary of Library Facilities</a>. This gives you a summary of
its syntax and a pointer to where you can find a more detailed
description. This appendix is particularly useful if you just want to
verify the order and type of arguments to a function, for example. It
also tells you what standard or system each function, variable, or macro
is derived from.
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