/usr/share/doc/flex-doc/html/Reentrant-Uses.html

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<a name="Reentrant-Uses"></a>
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<hr>
<a name="Uses-for-Reentrant-Scanners"></a>
<h3 class="section">19.1 Uses for Reentrant Scanners</h3>

<p>However, there are other uses for a reentrant scanner.  For example, you
could scan two or more files simultaneously to implement a <code>diff</code> at
the token level (i.e., instead of at the character level):
</p>
<a name="index-reentrant-scanners_002c-multiple-interleaved-scanners"></a>
<div class="example">
<pre class="verbatim">    /* Example of maintaining more than one active scanner. */

    do {
        int tok1, tok2;

        tok1 = yylex( scanner_1 );
        tok2 = yylex( scanner_2 );

        if( tok1 != tok2 )
            printf(&quot;Files are different.&quot;);

   } while ( tok1 &amp;&amp; tok2 );
</pre></div>

<p>Another use for a reentrant scanner is recursion.
(Note that a recursive scanner can also be created using a non-reentrant scanner and
buffer states. See <a href="Multiple-Input-Buffers.html#Multiple-Input-Buffers">Multiple Input Buffers</a>.)
</p>
<p>The following crude scanner supports the &lsquo;<samp>eval</samp>&rsquo; command by invoking
another instance of itself.
</p>
<a name="index-reentrant-scanners_002c-recursive-invocation"></a>
<div class="example">
<pre class="verbatim">    /* Example of recursive invocation. */

    %option reentrant

    %%
    &quot;eval(&quot;.+&quot;)&quot;  {
                      yyscan_t scanner;
                      YY_BUFFER_STATE buf;

                      yylex_init( &amp;scanner );
                      yytext[yyleng-1] = ' ';

                      buf = yy_scan_string( yytext + 5, scanner );
                      yylex( scanner );

                      yy_delete_buffer(buf,scanner);
                      yylex_destroy( scanner );
                 }
    ...
    %%
</pre></div>




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flex-doc 2.6.4-6 / usr / share / doc / flex-doc / html / Reentrant-Uses.html
