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<a name="A-Note-About-yytext-And-Memory-1"></a>
<h3 class="section">21.3 A Note About yytext And Memory</h3>

<a name="index-yytext_002c-memory-considerations"></a>

<p>When flex finds a match, <code>yytext</code> points to the first character of the
match in the input buffer. The string itself is part of the input buffer, and
is <em>NOT</em> allocated separately. The value of yytext will be overwritten the next
time yylex() is called. In short, the value of yytext is only valid from within
the matched rule&rsquo;s action.
</p>
<p>Often, you want the value of yytext to persist for later processing, i.e., by a
parser with non-zero lookahead. In order to preserve yytext, you will have to
copy it with strdup() or a similar function. But this introduces some headache
because your parser is now responsible for freeing the copy of yytext. If you
use a yacc or bison parser, (commonly used with flex), you will discover that
the error recovery mechanisms can cause memory to be leaked.
</p>
<p>To prevent memory leaks from strdup&rsquo;d yytext, you will have to track the memory
somehow. Our experience has shown that a garbage collection mechanism or a
pooled memory mechanism will save you a lot of grief when writing parsers.
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flex-doc 2.6.4-6 / usr / share / doc / flex-doc / html / A-Note-About-yytext-And-Memory.html
