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<h4 class="subsection">6.54.10 Diagnostic Pragmas</h4>

<p>GCC allows the user to selectively enable or disable certain types of
diagnostics, and change the kind of the diagnostic.  For example, a
project's policy might require that all sources compile with
<samp><span class="option">-Werror</span></samp> but certain files might have exceptions allowing
specific types of warnings.  Or, a project might selectively enable
diagnostics and treat them as errors depending on which preprocessor
macros are defined.

     <dl>
<dt><code>#pragma GCC diagnostic </code><var>kind</var> <var>option</var><dd><a name="index-pragma_002c-diagnostic-3140"></a>
Modifies the disposition of a diagnostic.  Note that not all
diagnostics are modifiable; at the moment only warnings (normally
controlled by &lsquo;<samp><span class="samp">-W...</span></samp>&rsquo;) can be controlled, and not all of them. 
Use <samp><span class="option">-fdiagnostics-show-option</span></samp> to determine which diagnostics
are controllable and which option controls them.

     <p><var>kind</var> is &lsquo;<samp><span class="samp">error</span></samp>&rsquo; to treat this diagnostic as an error,
&lsquo;<samp><span class="samp">warning</span></samp>&rsquo; to treat it like a warning (even if <samp><span class="option">-Werror</span></samp> is
in effect), or &lsquo;<samp><span class="samp">ignored</span></samp>&rsquo; if the diagnostic is to be ignored. 
<var>option</var> is a double quoted string which matches the command line
option.

     <pre class="example">          #pragma GCC diagnostic warning "-Wformat"
          #pragma GCC diagnostic error "-Wformat"
          #pragma GCC diagnostic ignored "-Wformat"
</pre>
     <p>Note that these pragmas override any command line options.  Also,
while it is syntactically valid to put these pragmas anywhere in your
sources, the only supported location for them is before any data or
functions are defined.  Doing otherwise may result in unpredictable
results depending on how the optimizer manages your sources.  If the
same option is listed multiple times, the last one specified is the
one that is in effect.  This pragma is not intended to be a general
purpose replacement for command line options, but for implementing
strict control over project policies.

 </dl>

 <p>GCC also offers a simple mechanism for printing messages during
compilation.

     <dl>
<dt><code>#pragma message </code><var>string</var><dd><a name="index-pragma_002c-diagnostic-3141"></a>
Prints <var>string</var> as a compiler message on compilation.  The message
is informational only, and is neither a compilation warning nor an error.

     <pre class="smallexample">          #pragma message "Compiling " __FILE__ "..."
</pre>
     <p><var>string</var> may be parenthesized, and is printed with location
information.  For example,

     <pre class="smallexample">          #define DO_PRAGMA(x) _Pragma (#x)
          #define TODO(x) DO_PRAGMA(message ("TODO - " #x))
          
          TODO(Remember to fix this)
</pre>
     <p>prints &lsquo;<samp><span class="samp">/tmp/file.c:4: note: #pragma message:
TODO - Remember to fix this</span></samp>&rsquo;.

 </dl>

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