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| <h3 class="section">6.45 Function Names as Strings</h3> |
| |
| <p><a name="index-g_t_0040code_007b_005f_005ffunc_005f_005f_007d-identifier-2605"></a><a name="index-g_t_0040code_007b_005f_005fFUNCTION_005f_005f_007d-identifier-2606"></a><a name="index-g_t_0040code_007b_005f_005fPRETTY_005fFUNCTION_005f_005f_007d-identifier-2607"></a> |
| GCC provides three magic variables which hold the name of the current |
| function, as a string. The first of these is <code>__func__</code>, which |
| is part of the C99 standard: |
| |
| <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 |
| |
| <pre class="smallexample"> static const char __func__[] = "function-name"; |
| </pre> |
| <p class="noindent">appeared, where function-name is the name of the lexically-enclosing |
| function. This name is the unadorned name of the function. |
| |
| <p><code>__FUNCTION__</code> is another name for <code>__func__</code>. Older |
| versions of GCC recognize only this name. However, it is not |
| standardized. For maximum portability, we recommend you use |
| <code>__func__</code>, but provide a fallback definition with the |
| preprocessor: |
| |
| <pre class="smallexample"> #if __STDC_VERSION__ < 199901L |
| # if __GNUC__ >= 2 |
| # define __func__ __FUNCTION__ |
| # else |
| # define __func__ "<unknown>" |
| # endif |
| #endif |
| </pre> |
| <p>In C, <code>__PRETTY_FUNCTION__</code> is yet another name for |
| <code>__func__</code>. However, in C++, <code>__PRETTY_FUNCTION__</code> contains |
| the type signature of the function as well as its bare name. For |
| example, this program: |
| |
| <pre class="smallexample"> extern "C" { |
| extern int printf (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> |
| <p class="noindent">gives this output: |
| |
| <pre class="smallexample"> __FUNCTION__ = sub |
| __PRETTY_FUNCTION__ = void a::sub(int) |
| </pre> |
| <p>These identifiers are not preprocessor macros. In GCC 3.3 and |
| earlier, in C only, <code>__FUNCTION__</code> and <code>__PRETTY_FUNCTION__</code> |
| were treated as string literals; they could be used to initialize |
| <code>char</code> arrays, and they could be concatenated with other string |
| literals. GCC 3.4 and later treat them as variables, like |
| <code>__func__</code>. In C++, <code>__FUNCTION__</code> and |
| <code>__PRETTY_FUNCTION__</code> have always been variables. |
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