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<h4 class="subsection">6.60.10 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-4178"></a>
Modifies the disposition of a diagnostic. Note that not all
diagnostics are modifiable; at the moment only warnings (normally
controlled by ‘<samp><span class="samp">-W...</span></samp>’) 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 ‘<samp><span class="samp">error</span></samp>’ to treat this diagnostic as an error,
‘<samp><span class="samp">warning</span></samp>’ to treat it like a warning (even if <samp><span class="option">-Werror</span></samp> is
in effect), or ‘<samp><span class="samp">ignored</span></samp>’ if the diagnostic is to be ignored.
<var>option</var> is a double quoted string that matches the command-line
option.
<pre class="smallexample"> #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. GCC keeps
track of the location of each pragma, and issues diagnostics according
to the state as of that point in the source file. Thus, pragmas occurring
after a line do not affect diagnostics caused by that line.
<br><dt><code>#pragma GCC diagnostic push</code><dt><code>#pragma GCC diagnostic pop</code><dd>
Causes GCC to remember the state of the diagnostics as of each
<code>push</code>, and restore to that point at each <code>pop</code>. If a
<code>pop</code> has no matching <code>push</code>, the command-line options are
restored.
<pre class="smallexample"> #pragma GCC diagnostic error "-Wuninitialized"
foo(a); /* error is given for this one */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuninitialized"
foo(b); /* no diagnostic for this one */
#pragma GCC diagnostic pop
foo(c); /* error is given for this one */
#pragma GCC diagnostic pop
foo(d); /* depends on command-line options */
</pre>
</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-4179"></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 class="noindent">prints ‘<samp><span class="samp">/tmp/file.c:4: note: #pragma message:
TODO - Remember to fix this</span></samp>’.
</dl>
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