ch08_69.htm

by Randal L. Schwartz and Tom Phoenix ISBN 0-596-00132-0 Third Edition, published July 2001. (See

#endif</pre></blockquote>

<p>which are used to determine if a constant will be defined.</p>
<p>A <tt class="literal">macro</tt> of <tt class="literal">1</tt> signals that the
constant is always defined, so the <tt class="literal">#if/#endif</tt> test
is omitted.
</p>
</dd>


<dt><b><tt class="literal">default</tt> </b></dt>
<dd>
Default value to use (instead of <tt class="literal">croak</tt> ing with
"your vendor has not defined . . . ) if the macro
isn't defined. Specifies a reference to an array
with type followed by value(s).
</p>
</dd>


<dt><b><tt class="literal">pre</tt>     </b></dt>
<dd>
C code to use before the assignment of the value of the constant.
This allows you to use temporary variables to extract a value from
part of a <tt class="literal">struct</tt> and return this as
<tt class="literal">value</tt>. This C code is placed at the start of a
block, so you can declare variables in it.
</p>
</dd>


<dt><b><tt class="literal">post</tt>    </b></dt>
<dd>
C code to place between the assignment of <tt class="literal">value</tt>
(temporary) and the return from the function. This allows you to
clear up anything in <tt class="literal">pre</tt>. Rarely needed.
</p>
</dd>


<dt><b><tt class="literal">def_pre</tt> </b></dt>
<dt><b><tt class="literal">def_post</tt>	</b></dt>
<dd>
Equivalents of <tt class="literal">pre</tt> and <tt class="literal">post</tt> for
the default value.
</p>
</dd>


<dt><b><tt class="literal">utf8</tt>    </b></dt>
<dd>
Generated internally. Is <tt class="literal">0</tt> or undefined if name is
7-bit ASCII, <tt class="literal">no</tt> if the name is 8-bit (and so
should match only if <tt class="literal">SvUTF8()</tt> is false), and
<tt class="literal">yes</tt> if the name is
<tt class="literal">utf8</tt>-encoded.
</p>
</dd>

</dl></div>

<a name="INDEX-1406" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>constant_types</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
constant_types
</pre><p>Returns a single scalar with <tt class="literal">#define</tt> definitions
for the constants used internally between the generated C and XS
functions.
</p></div>

<a name="INDEX-1407" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>C_stringify</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
C_stringify <em class="replaceable">name</em>
</pre><p>Returns a 7-bit ASCII correctly <tt class="literal">\</tt>-escaped version
of the string passed. Suitable for C <tt class="literal">""</tt> or
<tt class="literal">''</tt>. It will die if passed Unicode characters.
</p></div>

<a name="INDEX-1408" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>dump_names</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
dump_names <em class="replaceable">default_type</em>, <em class="replaceable">types</em>, <em class="replaceable">indent</em>, <em class="replaceable">options</em>, <em class="replaceable">item </em>...
</pre><p>An internal function to generate the embedded Perl code to regenerate
the constant subroutines. <em class="replaceable"><tt>default_type</tt></em>,
<em class="replaceable"><tt>types</tt></em>, and
<em class="replaceable"><tt>item</tt></em>s are the same as for
<tt class="literal">C_constant</tt>. <em class="replaceable"><tt>indent</tt></em> is
the number of spaces to indent. <em class="replaceable"><tt>options</tt></em> is
a hashref of options; currently, only
<tt class="literal">declare_types</tt> is recognized. If the value is true,
a <em class="replaceable"><tt>types</tt></em> is always declared in the
generated Perl code; if defined and false, one is never declared; and
if undefined, <em class="replaceable"><tt>types</tt></em> is declared only if
the values in <em class="replaceable"><tt>types</tt></em> as passed in cannot be
inferred from <em class="replaceable"><tt>default_types</tt></em> and the
<em class="replaceable"><tt>item</tt></em>s.
</p></div>

<a name="INDEX-1409" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>memEQ_clause </b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
memEQ_clause <em class="replaceable">name</em>, <em class="replaceable">checked_at</em>, <em class="replaceable">indent</em>
</pre><p>Returns a suitable C <tt class="literal">if</tt> statement to check whether
<em class="replaceable"><tt>name</tt></em> is equal to the C variable
<em class="replaceable"><tt>name</tt></em>. If
<em class="replaceable"><tt>checked_at</tt></em> is defined, then it is used to
avoid <tt class="literal">memEQ</tt> for short names.
</p></div>

<a name="INDEX-1410" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>params</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
params <em class="replaceable">what</em>
</pre><p>An internal function. <em class="replaceable">what</em> should be a
hashref of types the constant function will return.
<tt class="literal">params</tt> returns a hashref keyed <tt class="literal">IV NV PV
SV</tt> to show which combination of pointers will be needed in
the C argument list.
</p></div>

<a name="INDEX-1411" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>perl_stringify</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
perl_stringify <em class="replaceable">name</em>
</pre><p>Returns a 7-bit ASCII correctly <tt class="literal">\</tt>-escaped version
of the string passed. Suitable for a Perl <tt class="literal">""</tt>
string.
</p></div>

<a name="INDEX-1412" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>return_clause</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
return_clause <em class="replaceable">item</em>, <em class="replaceable">indent</em>
</pre><p>Returns a suitable <tt class="literal">#ifdef</tt> clause.
<em class="replaceable"><tt>item</tt></em> is a hashref passed to
<tt class="literal">C_constant</tt> and <tt class="literal">match_clause</tt>.
<em class="replaceable"><tt>indent</tt></em> is the number of spaces to indent;
defaulting is <tt class="literal">6</tt>.
</p></div>

<a name="INDEX-1413" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>switch_clause</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
switch_clause <em class="replaceable">indent</em>, <em class="replaceable">namelen</em>, <em class="replaceable">itemhash</em>, <em class="replaceable">item </em>...
</pre><p>An internal function to generate a suitable <tt class="literal">switch</tt>
clause, called by <tt class="literal">C_constant</tt>.
<em class="replaceable"><tt>item</tt></em>s are in the hashref format as given
in the description of <tt class="literal">C_constant</tt> and must all have
names of the same length, given by
<em class="replaceable"><tt>namelen</tt></em>.
<em class="replaceable"><tt>itemhash</tt></em> is a reference to a hash, keyed
by name, with values as the hashrefs in the
<em class="replaceable"><tt>item</tt></em> list.
</p></div>

<a name="INDEX-1414" /><div class="refentry"><table width="515" border="0" cellpadding="5"><tr><td align="left"><font size="+1"><b>XS_constant</b></font></td><td align="right"><i></i></td></tr></table><hr width="515" size="3" noshade="true" align="left" color="black" /><pre>
XS_constant <em class="replaceable">package</em>, <em class="replaceable">types</em>, <em class="replaceable">subname</em>, <em class="replaceable">c_subname</em>
</pre><p>Generates the XS code to implement the Perl subroutine
<em class="replaceable"><tt>package</tt></em><tt class="literal">::constant</tt> used
by <em class="replaceable"><tt>package</tt></em><tt class="literal">::AUTOLOAD</tt> to
load constants. This XS code is a wrapper around a C subroutine
usually generated by <tt class="literal">C_constant</tt> and usually named
<tt class="literal">constant</tt>
</p><p><em class="replaceable"><tt>types</tt></em> should be given either as a
comma-separated list of types that the C subroutine
<tt class="literal">constant</tt> will generate or as a reference to a
hash. It should be the same list of types that
<tt class="literal">C_constant</tt> was given. Otherwise,
<tt class="literal">XS_constant</tt> and <tt class="literal">C_constant</tt> may
have different ideas about the number of parameters passed to the C
function <tt class="literal">constant</tt>.
</p><p>You can call the Perl visible subroutine something other than
"constant" if you give the
parameter <em class="replaceable"><tt>subname</tt></em>. The C subroutine it
calls defaults to the name of the Perl visible subroutine, unless you
give the parameter <em class="replaceable"><tt>c_subname</tt></em>.
</p></div>

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