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<title>Using the GNU Compiler Collection (GCC): Function Names</title>
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<a name="Function-Names"></a>
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<p>
Next: <a href="Return-Address.html#Return-Address" accesskey="n" rel="next">Return Address</a>, Previous: <a href="Incomplete-Enums.html#Incomplete-Enums" accesskey="p" rel="previous">Incomplete Enums</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Function-Names-as-Strings"></a>
<h3 class="section">6.50 Function Names as Strings</h3>
<a name="index-_005f_005ffunc_005f_005f-identifier"></a>
<a name="index-_005f_005fFUNCTION_005f_005f-identifier"></a>
<a name="index-_005f_005fPRETTY_005fFUNCTION_005f_005f-identifier"></a>
<p>GCC provides three magic constants that hold the name of the current
function as a string. In C++11 and later modes, all three are treated
as constant expressions and can be used in <code>constexpr</code> constexts.
The first of these constants is <code>__func__</code>, which is part of
the C99 standard:
</p>
<p>The identifier <code>__func__</code> is implicitly declared by the translator
as if, immediately following the opening brace of each function
definition, the declaration
</p>
<div class="smallexample">
<pre class="smallexample">static const char __func__[] = "function-name";
</pre></div>
<p>appeared, where function-name is the name of the lexically-enclosing
function. This name is the unadorned name of the function. As an
extension, at file (or, in C++, namespace scope), <code>__func__</code>
evaluates to the empty string.
</p>
<p><code>__FUNCTION__</code> is another name for <code>__func__</code>, provided for
backward compatibility with old versions of GCC.
</p>
<p>In C, <code>__PRETTY_FUNCTION__</code> is yet another name for
<code>__func__</code>, except that at file scope (or, in C++, namespace scope),
it evaluates to the string <code>"top level"</code>. In addition, in C++,
<code>__PRETTY_FUNCTION__</code> contains the signature of the function as
well as its bare name. For example, this program:
</p>
<div class="smallexample">
<pre class="smallexample">extern "C" int printf (const char *, ...);
class a {
public:
void sub (int i)
{
printf ("__FUNCTION__ = %s\n", __FUNCTION__);
printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
}
};
int
main (void)
{
a ax;
ax.sub (0);
return 0;
}
</pre></div>
<p>gives this output:
</p>
<div class="smallexample">
<pre class="smallexample">__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)
</pre></div>
<p>These identifiers are variables, not preprocessor macros, and may not
be used to initialize <code>char</code> arrays or be concatenated with string
literals.
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