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152 lines
6.1 KiB
HTML
152 lines
6.1 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Function Names (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Function Names (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Function Names (Using the GNU Compiler Collection (GCC))">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">
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<link href="Return-Address.html#Return-Address" rel="next" title="Return Address">
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<link href="Incomplete-Enums.html#Incomplete-Enums" rel="prev" title="Incomplete Enums">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Function-Names"></a>
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<div class="header">
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<p>
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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="prev">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="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Function-Names-as-Strings"></a>
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<h3 class="section">6.48 Function Names as Strings</h3>
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<a name="index-_005f_005ffunc_005f_005f-identifier"></a>
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<a name="index-_005f_005fFUNCTION_005f_005f-identifier"></a>
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<a name="index-_005f_005fPRETTY_005fFUNCTION_005f_005f-identifier"></a>
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<p>GCC provides three magic constants that hold the name of the current
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function as a string. In C++11 and later modes, all three are treated
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as constant expressions and can be used in <code>constexpr</code> constexts.
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The first of these constants is <code>__func__</code>, which is part of
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the C99 standard:
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</p>
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<p>The identifier <code>__func__</code> is implicitly declared by the translator
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as if, immediately following the opening brace of each function
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definition, the declaration
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</p>
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<div class="smallexample">
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<pre class="smallexample">static const char __func__[] = "function-name";
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</pre></div>
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<p>appeared, where function-name is the name of the lexically-enclosing
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function. This name is the unadorned name of the function. As an
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extension, at file (or, in C++, namespace scope), <code>__func__</code>
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evaluates to the empty string.
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</p>
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<p><code>__FUNCTION__</code> is another name for <code>__func__</code>, provided for
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backward compatibility with old versions of GCC.
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</p>
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<p>In C, <code>__PRETTY_FUNCTION__</code> is yet another name for
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<code>__func__</code>, except that at file (or, in C++, namespace scope),
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it evaluates to the string <code>"top level"</code>. In addition, in C++,
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<code>__PRETTY_FUNCTION__</code> contains the signature of the function as
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well as its bare name. For example, this program:
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</p>
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<div class="smallexample">
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<pre class="smallexample">extern "C" int printf (const char *, ...);
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class a {
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public:
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void sub (int i)
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{
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printf ("__FUNCTION__ = %s\n", __FUNCTION__);
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printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
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}
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};
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int
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main (void)
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{
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a ax;
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ax.sub (0);
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return 0;
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}
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</pre></div>
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<p>gives this output:
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</p>
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<div class="smallexample">
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<pre class="smallexample">__FUNCTION__ = sub
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__PRETTY_FUNCTION__ = void a::sub(int)
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</pre></div>
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<p>These identifiers are variables, not preprocessor macros, and may not
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be used to initialize <code>char</code> arrays or be concatenated with string
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literals.
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</p>
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<hr>
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<div class="header">
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<p>
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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="prev">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="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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