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153 lines
7.0 KiB
HTML
153 lines
7.0 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>Microsoft Windows Variable Attributes (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Microsoft Windows Variable Attributes (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Microsoft Windows Variable Attributes (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="Variable-Attributes.html#Variable-Attributes" rel="up" title="Variable Attributes">
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<link href="MSP430-Variable-Attributes.html#MSP430-Variable-Attributes" rel="next" title="MSP430 Variable Attributes">
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<link href="MeP-Variable-Attributes.html#MeP-Variable-Attributes" rel="prev" title="MeP Variable Attributes">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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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="Microsoft-Windows-Variable-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="MSP430-Variable-Attributes.html#MSP430-Variable-Attributes" accesskey="n" rel="next">MSP430 Variable Attributes</a>, Previous: <a href="MeP-Variable-Attributes.html#MeP-Variable-Attributes" accesskey="p" rel="prev">MeP Variable Attributes</a>, Up: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="u" rel="up">Variable Attributes</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="Microsoft-Windows-Variable-Attributes-1"></a>
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<h4 class="subsection">6.32.9 Microsoft Windows Variable Attributes</h4>
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<p>You can use these attributes on Microsoft Windows targets.
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<a href="x86-Variable-Attributes.html#x86-Variable-Attributes">x86 Variable Attributes</a> for additional Windows compatibility
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attributes available on all x86 targets.
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</p>
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<dl compact="compact">
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<dt><code>dllimport</code></dt>
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<dt><code>dllexport</code></dt>
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<dd><a name="index-dllimport-variable-attribute"></a>
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<a name="index-dllexport-variable-attribute"></a>
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<p>The <code>dllimport</code> and <code>dllexport</code> attributes are described in
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<a href="Microsoft-Windows-Function-Attributes.html#Microsoft-Windows-Function-Attributes">Microsoft Windows Function Attributes</a>.
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</p>
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</dd>
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<dt><code>selectany</code></dt>
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<dd><a name="index-selectany-variable-attribute"></a>
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<p>The <code>selectany</code> attribute causes an initialized global variable to
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have link-once semantics. When multiple definitions of the variable are
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encountered by the linker, the first is selected and the remainder are
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discarded. Following usage by the Microsoft compiler, the linker is told
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<em>not</em> to warn about size or content differences of the multiple
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definitions.
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</p>
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<p>Although the primary usage of this attribute is for POD types, the
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attribute can also be applied to global C++ objects that are initialized
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by a constructor. In this case, the static initialization and destruction
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code for the object is emitted in each translation defining the object,
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but the calls to the constructor and destructor are protected by a
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link-once guard variable.
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</p>
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<p>The <code>selectany</code> attribute is only available on Microsoft Windows
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targets. You can use <code>__declspec (selectany)</code> as a synonym for
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<code>__attribute__ ((selectany))</code> for compatibility with other
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compilers.
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</p>
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</dd>
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<dt><code>shared</code></dt>
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<dd><a name="index-shared-variable-attribute"></a>
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<p>On Microsoft Windows, in addition to putting variable definitions in a named
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section, the section can also be shared among all running copies of an
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executable or DLL. For example, this small program defines shared data
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by putting it in a named section <code>shared</code> and marking the section
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shareable:
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</p>
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<div class="smallexample">
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<pre class="smallexample">int foo __attribute__((section ("shared"), shared)) = 0;
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int
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main()
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{
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/* <span class="roman">Read and write foo. All running
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copies see the same value.</span> */
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return 0;
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}
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</pre></div>
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<p>You may only use the <code>shared</code> attribute along with <code>section</code>
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attribute with a fully-initialized global definition because of the way
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linkers work. See <code>section</code> attribute for more information.
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</p>
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<p>The <code>shared</code> attribute is only available on Microsoft Windows.
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</p>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="MSP430-Variable-Attributes.html#MSP430-Variable-Attributes" accesskey="n" rel="next">MSP430 Variable Attributes</a>, Previous: <a href="MeP-Variable-Attributes.html#MeP-Variable-Attributes" accesskey="p" rel="prev">MeP Variable Attributes</a>, Up: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="u" rel="up">Variable Attributes</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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