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206 lines
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206 lines
14 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 Attributes (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Function Attributes (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Function Attributes (Using the GNU Compiler Collection (GCC))">
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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="Common-Function-Attributes.html#Common-Function-Attributes" rel="next" title="Common Function Attributes">
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</head>
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<body lang="en">
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<a name="Function-Attributes"></a>
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<div class="header">
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<p>
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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>
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</div>
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<hr>
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<a name="Declaring-Attributes-of-Functions"></a>
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<h3 class="section">6.31 Declaring Attributes of Functions</h3>
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<a name="index-function-attributes"></a>
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<a name="index-declaring-attributes-of-functions"></a>
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<a name="index-volatile-applied-to-function"></a>
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<a name="index-const-applied-to-function"></a>
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<p>In GNU C, you can use function attributes to declare certain things
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about functions called in your program which help the compiler
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optimize calls and check your code more carefully. For example, you
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can use attributes to declare that a function never returns
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(<code>noreturn</code>), returns a value depending only on its arguments
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(<code>pure</code>), or has <code>printf</code>-style arguments (<code>format</code>).
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</p>
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<p>You can also use attributes to control memory placement, code
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generation options or call/return conventions within the function
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being annotated. Many of these attributes are target-specific. For
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example, many targets support attributes for defining interrupt
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handler functions, which typically must follow special register usage
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and return conventions.
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</p>
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<p>Function attributes are introduced by the <code>__attribute__</code> keyword
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on a declaration, followed by an attribute specification inside double
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parentheses. You can specify multiple attributes in a declaration by
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separating them by commas within the double parentheses or by
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immediately following an attribute declaration with another attribute
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declaration. See <a href="Attribute-Syntax.html#Attribute-Syntax">Attribute Syntax</a>, for the exact rules on attribute
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syntax and placement. Compatible attribute specifications on distinct
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declarations of the same function are merged. An attribute specification
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that is not compatible with attributes already applied to a declaration
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of the same function is ignored with a warning.
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</p>
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<p>GCC also supports attributes on
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variable declarations (see <a href="Variable-Attributes.html#Variable-Attributes">Variable Attributes</a>),
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labels (see <a href="Label-Attributes.html#Label-Attributes">Label Attributes</a>),
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enumerators (see <a href="Enumerator-Attributes.html#Enumerator-Attributes">Enumerator Attributes</a>),
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statements (see <a href="Statement-Attributes.html#Statement-Attributes">Statement Attributes</a>),
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and types (see <a href="Type-Attributes.html#Type-Attributes">Type Attributes</a>).
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</p>
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<p>There is some overlap between the purposes of attributes and pragmas
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(see <a href="Pragmas.html#Pragmas">Pragmas Accepted by GCC</a>). It has been
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found convenient to use <code>__attribute__</code> to achieve a natural
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attachment of attributes to their corresponding declarations, whereas
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<code>#pragma</code> is of use for compatibility with other compilers
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or constructs that do not naturally form part of the grammar.
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</p>
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<p>In addition to the attributes documented here,
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GCC plugins may provide their own attributes.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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<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">
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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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>
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</div>
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</body>
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</html>
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