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<a name="Misc-Macros"></a>
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<a name="Miscellaneous-Macros"></a>
<h2 class="chapter">13 Miscellaneous Macros</h2>

<a name="index-YY_005fUSER_005fACTION"></a>
<p>The macro <code>YY_USER_ACTION</code> can be defined to provide an action
which is always executed prior to the matched rule&rsquo;s action.  For
example, it could be #define&rsquo;d to call a routine to convert yytext to
lower-case.  When <code>YY_USER_ACTION</code> is invoked, the variable
<code>yy_act</code> gives the number of the matched rule (rules are numbered
starting with 1).  Suppose you want to profile how often each of your
rules is matched.  The following would do the trick:
</p>
<a name="index-YY_005fUSER_005fACTION-to-track-each-time-a-rule-is-matched"></a>
<div class="example">
<pre class="verbatim">    #define YY_USER_ACTION ++ctr[yy_act]
</pre></div>

<a name="index-YY_005fNUM_005fRULES"></a>
<p>where <code>ctr</code> is an array to hold the counts for the different rules.
Note that the macro <code>YY_NUM_RULES</code> gives the total number of rules
(including the default rule), even if you use &lsquo;<samp>-s)</samp>&rsquo;, so a correct
declaration for <code>ctr</code> is:
</p>
<div class="example">
<pre class="verbatim">    int ctr[YY_NUM_RULES];
</pre></div>

<a name="index-YY_005fUSER_005fINIT"></a>
<p>The macro <code>YY_USER_INIT</code> may be defined to provide an action which
is always executed before the first scan (and before the scanner&rsquo;s
internal initializations are done).  For example, it could be used to
call a routine to read in a data table or open a logging file.
</p>
<a name="index-yy_005fset_005finteractive"></a>
<p>The macro <code>yy_set_interactive(is_interactive)</code> can be used to
control whether the current buffer is considered <em>interactive</em>.  An
interactive buffer is processed more slowly, but must be used when the
scanner&rsquo;s input source is indeed interactive to avoid problems due to
waiting to fill buffers (see the discussion of the &lsquo;<samp>-I</samp>&rsquo; flag in
<a href="Scanner-Options.html#Scanner-Options">Scanner Options</a>).  A non-zero value in the macro invocation marks
the buffer as interactive, a zero value as non-interactive.  Note that
use of this macro overrides <code>%option always-interactive</code> or
<code>%option never-interactive</code> (see <a href="Scanner-Options.html#Scanner-Options">Scanner Options</a>).
<code>yy_set_interactive()</code> must be invoked prior to beginning to scan
the buffer that is (or is not) to be considered interactive.
</p>
<a name="index-BOL_002c-setting-it"></a>
<a name="index-yy_005fset_005fbol"></a>
<p>The macro <code>yy_set_bol(at_bol)</code> can be used to control whether the
current buffer&rsquo;s scanning context for the next token match is done as
though at the beginning of a line.  A non-zero macro argument makes
rules anchored with &lsquo;<samp>^</samp>&rsquo; active, while a zero argument makes
&lsquo;<samp>^</samp>&rsquo; rules inactive.
</p>
<a name="index-BOL_002c-checking-the-BOL-flag"></a>
<a name="index-YY_005fAT_005fBOL"></a>
<p>The macro <code>YY_AT_BOL()</code> returns true if the next token scanned from
the current buffer will have &lsquo;<samp>^</samp>&rsquo; rules active, false otherwise.
</p>
<a name="index-actions_002c-redefining-YY_005fBREAK"></a>
<a name="index-YY_005fBREAK"></a>
<p>In the generated scanner, the actions are all gathered in one large
switch statement and separated using <code>YY_BREAK</code>, which may be
redefined.  By default, it is simply a <code>break</code>, to separate each
rule&rsquo;s action from the following rule&rsquo;s.  Redefining <code>YY_BREAK</code>
allows, for example, C++ users to #define YY_BREAK to do nothing (while
being very careful that every rule ends with a <code>break</code> or a
<code>return</code>!) to avoid suffering from unreachable statement warnings
where because a rule&rsquo;s action ends with <code>return</code>, the
<code>YY_BREAK</code> is inaccessible.
</p>
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