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<a name="Missing"></a>
<div class="header">
<p>
Next: <a href="Makefile-Conventions.html#Makefile-Conventions" accesskey="n" rel="next">Makefile Conventions</a>, Previous: <a href="Features.html#Features" accesskey="p" rel="prev">Features</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<a name="Incompatibilities-and-Missing-Features"></a>
<h2 class="chapter">15 Incompatibilities and Missing Features</h2>
<a name="index-incompatibilities"></a>
<a name="index-missing-features"></a>
<a name="index-features_002c-missing"></a>

<p>The <code>make</code> programs in various other systems support a few features
that are not implemented in GNU <code>make</code>.  The POSIX.2 standard
(<cite>IEEE Standard 1003.2-1992</cite>) which specifies <code>make</code> does not
require any of these features.
</p>
<ul>
<li> A target of the form &lsquo;<samp><var>file</var>((<var>entry</var>))</samp>&rsquo; stands for a member
of archive file <var>file</var>.  The member is chosen, not by name, but by
being an object file which defines the linker symbol <var>entry</var>.

<p>This feature was not put into GNU <code>make</code> because of the
non-modularity of putting knowledge into <code>make</code> of the internal
format of archive file symbol tables.
See <a href="Archives.html#Archive-Symbols">Updating Archive Symbol Directories</a>.
</p>
</li><li> Suffixes (used in suffix rules) that end with the character &lsquo;<samp>~</samp>&rsquo;
have a special meaning to System V <code>make</code>;
they refer to the SCCS file that corresponds
to the file one would get without the &lsquo;<samp>~</samp>&rsquo;.  For example, the
suffix rule &lsquo;<samp>.c~.o</samp>&rsquo; would make the file <samp><var>n</var>.o</samp> from
the SCCS file <samp>s.<var>n</var>.c</samp>.  For complete coverage, a whole
series of such suffix rules is required.
See <a href="Implicit-Rules.html#Suffix-Rules">Old-Fashioned Suffix Rules</a>.

<p>In GNU <code>make</code>, this entire series of cases is handled by two
pattern rules for extraction from SCCS, in combination with the
general feature of rule chaining.
See <a href="Implicit-Rules.html#Chained-Rules">Chains of Implicit Rules</a>.
</p>
</li><li> In System V and 4.3 BSD <code>make</code>, files found by <code>VPATH</code>
search (see <a href="Rules.html#Directory-Search">Searching Directories for
Prerequisites</a>) have their names changed inside recipes.  We feel it
is much cleaner to always use automatic variables and thus make this
feature obsolete.

</li><li> In some Unix <code>make</code>s, the automatic variable <code>$*</code> appearing in
the prerequisites of a rule has the amazingly strange &ldquo;feature&rdquo; of
expanding to the full name of the <em>target of that rule</em>.  We cannot
imagine what went on in the minds of Unix <code>make</code> developers to do
this; it is utterly inconsistent with the normal definition of <code>$*</code>.
<a name="index-_002a-_0028automatic-variable_0029_002c-unsupported-bizarre-usage"></a>

</li><li> In some Unix <code>make</code>s, implicit rule search (see <a href="Implicit-Rules.html#Implicit-Rules">Using Implicit Rules</a>) is apparently done for <em>all</em>
targets, not just those without recipes.  This means you can
do:

<div class="example">
<pre class="example">foo.o:
        cc -c foo.c
</pre></div>

<p>and Unix <code>make</code> will intuit that <samp>foo.o</samp> depends on
<samp>foo.c</samp>.
</p>
<p>We feel that such usage is broken.  The prerequisite properties of
<code>make</code> are well-defined (for GNU <code>make</code>, at least),
and doing such a thing simply does not fit the model.
</p>
</li><li> GNU <code>make</code> does not include any built-in implicit rules for
compiling or preprocessing EFL programs.  If we hear of anyone who is
using EFL, we will gladly add them.

</li><li> It appears that in SVR4 <code>make</code>, a suffix rule can be specified
with no recipe, and it is treated as if it had an empty recipe
(see <a href="Recipes.html#Empty-Recipes">Empty Recipes</a>).  For example:

<div class="example">
<pre class="example">.c.a:
</pre></div>

<p>will override the built-in <samp>.c.a</samp> suffix rule.
</p>
<p>We feel that it is cleaner for a rule without a recipe to always simply
add to the prerequisite list for the target.  The above example can be
easily rewritten to get the desired behavior in GNU <code>make</code>:
</p>
<div class="example">
<pre class="example">.c.a: ;
</pre></div>

</li><li> Some versions of <code>make</code> invoke the shell with the &lsquo;<samp>-e</samp>&rsquo; flag,
except under &lsquo;<samp>-k</samp>&rsquo; (see <a href="Running.html#Testing">Testing the Compilation of a
Program</a>).  The &lsquo;<samp>-e</samp>&rsquo; flag tells the shell to exit as soon as any
program it runs returns a nonzero status.  We feel it is cleaner to
write each line of the recipe to stand on its own and not require this
special treatment.
</li></ul>


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Next: <a href="Makefile-Conventions.html#Makefile-Conventions" accesskey="n" rel="next">Makefile Conventions</a>, Previous: <a href="Features.html#Features" accesskey="p" rel="prev">Features</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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