You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
206 lines
14 KiB
HTML
206 lines
14 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
|
(see below). A copy of the license is included in the section entitled
|
|
"GNU Free Documentation License".
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development. -->
|
|
<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>Function Attributes (Using the GNU Compiler Collection (GCC))</title>
|
|
|
|
<meta name="description" content="Function Attributes (Using the GNU Compiler Collection (GCC))">
|
|
<meta name="keywords" content="Function Attributes (Using the GNU Compiler Collection (GCC))">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<link href="index.html#Top" rel="start" title="Top">
|
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">
|
|
<link href="Common-Function-Attributes.html#Common-Function-Attributes" rel="next" title="Common Function Attributes">
|
|
<link href="Mixed-Declarations.html#Mixed-Declarations" rel="prev" title="Mixed Declarations">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
div.smalllisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
|
pre.smallexample {font-size: smaller}
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
|
pre.smalllisp {font-size: smaller}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<a name="Function-Attributes"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="n" rel="next">Variable Attributes</a>, Previous: <a href="Mixed-Declarations.html#Mixed-Declarations" accesskey="p" rel="prev">Mixed Declarations</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>
|
|
</div>
|
|
<hr>
|
|
<a name="Declaring-Attributes-of-Functions"></a>
|
|
<h3 class="section">6.31 Declaring Attributes of Functions</h3>
|
|
<a name="index-function-attributes"></a>
|
|
<a name="index-declaring-attributes-of-functions"></a>
|
|
<a name="index-volatile-applied-to-function"></a>
|
|
<a name="index-const-applied-to-function"></a>
|
|
|
|
<p>In GNU C, you can use function attributes to declare certain things
|
|
about functions called in your program which help the compiler
|
|
optimize calls and check your code more carefully. For example, you
|
|
can use attributes to declare that a function never returns
|
|
(<code>noreturn</code>), returns a value depending only on its arguments
|
|
(<code>pure</code>), or has <code>printf</code>-style arguments (<code>format</code>).
|
|
</p>
|
|
<p>You can also use attributes to control memory placement, code
|
|
generation options or call/return conventions within the function
|
|
being annotated. Many of these attributes are target-specific. For
|
|
example, many targets support attributes for defining interrupt
|
|
handler functions, which typically must follow special register usage
|
|
and return conventions.
|
|
</p>
|
|
<p>Function attributes are introduced by the <code>__attribute__</code> keyword
|
|
on a declaration, followed by an attribute specification inside double
|
|
parentheses. You can specify multiple attributes in a declaration by
|
|
separating them by commas within the double parentheses or by
|
|
immediately following an attribute declaration with another attribute
|
|
declaration. See <a href="Attribute-Syntax.html#Attribute-Syntax">Attribute Syntax</a>, for the exact rules on attribute
|
|
syntax and placement. Compatible attribute specifications on distinct
|
|
declarations of the same function are merged. An attribute specification
|
|
that is not compatible with attributes already applied to a declaration
|
|
of the same function is ignored with a warning.
|
|
</p>
|
|
<p>GCC also supports attributes on
|
|
variable declarations (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>),
|
|
labels (see <a href="Label-Attributes.html#Label-Attributes">Label Attributes</a>),
|
|
enumerators (see <a href="Enumerator-Attributes.html#Enumerator-Attributes">Enumerator Attributes</a>),
|
|
statements (see <a href="Statement-Attributes.html#Statement-Attributes">Statement Attributes</a>),
|
|
and types (see <a href="Type-Attributes.html#Type-Attributes">Type Attributes</a>).
|
|
</p>
|
|
<p>There is some overlap between the purposes of attributes and pragmas
|
|
(see <a href="Pragmas.html#Pragmas">Pragmas Accepted by GCC</a>). It has been
|
|
found convenient to use <code>__attribute__</code> to achieve a natural
|
|
attachment of attributes to their corresponding declarations, whereas
|
|
<code>#pragma</code> is of use for compatibility with other compilers
|
|
or constructs that do not naturally form part of the grammar.
|
|
</p>
|
|
<p>In addition to the attributes documented here,
|
|
GCC plugins may provide their own attributes.
|
|
</p>
|
|
<table class="menu" border="0" cellspacing="0">
|
|
<tr><td align="left" valign="top">• <a href="Common-Function-Attributes.html#Common-Function-Attributes" accesskey="1">Common Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="AArch64-Function-Attributes.html#AArch64-Function-Attributes" accesskey="2">AArch64 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="ARC-Function-Attributes.html#ARC-Function-Attributes" accesskey="3">ARC Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="ARM-Function-Attributes.html#ARM-Function-Attributes" accesskey="4">ARM Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="AVR-Function-Attributes.html#AVR-Function-Attributes" accesskey="5">AVR Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Blackfin-Function-Attributes.html#Blackfin-Function-Attributes" accesskey="6">Blackfin Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="CR16-Function-Attributes.html#CR16-Function-Attributes" accesskey="7">CR16 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Epiphany-Function-Attributes.html#Epiphany-Function-Attributes" accesskey="8">Epiphany Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="H8_002f300-Function-Attributes.html#H8_002f300-Function-Attributes" accesskey="9">H8/300 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="IA_002d64-Function-Attributes.html#IA_002d64-Function-Attributes">IA-64 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="M32C-Function-Attributes.html#M32C-Function-Attributes">M32C Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="M32R_002fD-Function-Attributes.html#M32R_002fD-Function-Attributes">M32R/D Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="m68k-Function-Attributes.html#m68k-Function-Attributes">m68k Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="MCORE-Function-Attributes.html#MCORE-Function-Attributes">MCORE Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="MeP-Function-Attributes.html#MeP-Function-Attributes">MeP Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="MicroBlaze-Function-Attributes.html#MicroBlaze-Function-Attributes">MicroBlaze Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Microsoft-Windows-Function-Attributes.html#Microsoft-Windows-Function-Attributes">Microsoft Windows Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="MIPS-Function-Attributes.html#MIPS-Function-Attributes">MIPS Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="MSP430-Function-Attributes.html#MSP430-Function-Attributes">MSP430 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="NDS32-Function-Attributes.html#NDS32-Function-Attributes">NDS32 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Nios-II-Function-Attributes.html#Nios-II-Function-Attributes">Nios II Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Nvidia-PTX-Function-Attributes.html#Nvidia-PTX-Function-Attributes">Nvidia PTX Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="PowerPC-Function-Attributes.html#PowerPC-Function-Attributes">PowerPC Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="RISC_002dV-Function-Attributes.html#RISC_002dV-Function-Attributes">RISC-V Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="RL78-Function-Attributes.html#RL78-Function-Attributes">RL78 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="RX-Function-Attributes.html#RX-Function-Attributes">RX Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="S_002f390-Function-Attributes.html#S_002f390-Function-Attributes">S/390 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="SH-Function-Attributes.html#SH-Function-Attributes">SH Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="SPU-Function-Attributes.html#SPU-Function-Attributes">SPU Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Symbian-OS-Function-Attributes.html#Symbian-OS-Function-Attributes">Symbian OS Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="V850-Function-Attributes.html#V850-Function-Attributes">V850 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Visium-Function-Attributes.html#Visium-Function-Attributes">Visium Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="x86-Function-Attributes.html#x86-Function-Attributes">x86 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
<tr><td align="left" valign="top">• <a href="Xstormy16-Function-Attributes.html#Xstormy16-Function-Attributes">Xstormy16 Function Attributes</a>:</td><td> </td><td align="left" valign="top">
|
|
</td></tr>
|
|
</table>
|
|
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="n" rel="next">Variable Attributes</a>, Previous: <a href="Mixed-Declarations.html#Mixed-Declarations" accesskey="p" rel="prev">Mixed Declarations</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>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|