document #error and #warning including cpperraswarn/nocpperraswarn

git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@8297 626c5289-ae23-0410-ae9c-e8d60b6d4f22

Doc/Manual/Preprocessor.html

@@ -19,6 +19,7 @@
 <li><a href="#Preprocessor_nn8">Preprocessing and %{ ... %} blocks</a>
 <li><a href="#Preprocessor_nn9">Preprocessing and { ... }</a>
 <li><a href="#Preprocessor_nn10">Viewing preprocessor output</a>
+<li><a href="#Preprocessor_warning_error">The #error and #warning directives</a>
 </ul>
 </div>
 <!-- INDEX -->
@@ -381,5 +382,34 @@ Instead the results after the preprocessor has run are displayed.
 This might be useful as an aid to debugging and viewing the results of macro expansions.
 </p>
 
+<H2><a name="Preprocessor_warning_error"></a>7.10 The #error and #warning directives</H2>
+<p>
+SWIG supports the commonly used <tt>#warning</tt> and <tt>#error</tt> preprocessor directives.
+The <tt>#warning</tt> directive will cause SWIG to issue a warning then continue processing.
+The <tt>#error</tt> directive will cause SWIG to exit with a fatal error.
+Example usage:
+</p>
+
+<div class="code">
+<pre>
+#error "This is a fatal error message"
+#warning "This is a warning message"
+</pre>
+</div>
+
+<p>
+The <tt>#error</tt> behaviour can be made to work like <tt>#warning</tt> if the <tt>-cpperraswarn</tt>
+commandline option is used. Alternatively, the <tt>#pragma</tt> directive can be used to the same effect, for example:
+</p>
+
+<div class="code">
+<pre>
+  /* Modified behaviour: #error does not cause SWIG to exit with error */
+  #pragma SWIG cpperraswarn=1
+  /* Normal behaviour: #error does cause SWIG to exit with error */
+  #pragma SWIG cpperraswarn=0
+</pre>
+</div>
+
 </body>
 </html>