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146 lines
7.3 KiB
HTML
146 lines
7.3 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>Complex (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Complex (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Complex (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="Floating-Types.html#Floating-Types" rel="next" title="Floating Types">
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<link href="Long-Long.html#Long-Long" rel="prev" title="Long Long">
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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="Complex"></a>
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<div class="header">
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<p>
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Next: <a href="Floating-Types.html#Floating-Types" accesskey="n" rel="next">Floating Types</a>, Previous: <a href="Long-Long.html#Long-Long" accesskey="p" rel="prev">Long Long</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="Complex-Numbers"></a>
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<h3 class="section">6.10 Complex Numbers</h3>
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<a name="index-complex-numbers"></a>
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<a name="index-_005fComplex-keyword"></a>
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<a name="index-_005f_005fcomplex_005f_005f-keyword"></a>
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<p>ISO C99 supports complex floating data types, and as an extension GCC
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supports them in C90 mode and in C++. GCC also supports complex integer data
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types which are not part of ISO C99. You can declare complex types
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using the keyword <code>_Complex</code>. As an extension, the older GNU
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keyword <code>__complex__</code> is also supported.
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</p>
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<p>For example, ‘<samp>_Complex double x;</samp>’ declares <code>x</code> as a
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variable whose real part and imaginary part are both of type
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<code>double</code>. ‘<samp>_Complex short int y;</samp>’ declares <code>y</code> to
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have real and imaginary parts of type <code>short int</code>; this is not
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likely to be useful, but it shows that the set of complex types is
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complete.
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</p>
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<p>To write a constant with a complex data type, use the suffix ‘<samp>i</samp>’ or
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‘<samp>j</samp>’ (either one; they are equivalent). For example, <code>2.5fi</code>
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has type <code>_Complex float</code> and <code>3i</code> has type
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<code>_Complex int</code>. Such a constant always has a pure imaginary
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value, but you can form any complex value you like by adding one to a
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real constant. This is a GNU extension; if you have an ISO C99
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conforming C library (such as the GNU C Library), and want to construct complex
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constants of floating type, you should include <code><complex.h></code> and
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use the macros <code>I</code> or <code>_Complex_I</code> instead.
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</p>
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<p>The ISO C++14 library also defines the ‘<samp>i</samp>’ suffix, so C++14 code
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that includes the ‘<samp><complex></samp>’ header cannot use ‘<samp>i</samp>’ for the
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GNU extension. The ‘<samp>j</samp>’ suffix still has the GNU meaning.
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</p>
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<a name="index-_005f_005freal_005f_005f-keyword"></a>
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<a name="index-_005f_005fimag_005f_005f-keyword"></a>
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<p>To extract the real part of a complex-valued expression <var>exp</var>, write
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<code>__real__ <var>exp</var></code>. Likewise, use <code>__imag__</code> to
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extract the imaginary part. This is a GNU extension; for values of
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floating type, you should use the ISO C99 functions <code>crealf</code>,
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<code>creal</code>, <code>creall</code>, <code>cimagf</code>, <code>cimag</code> and
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<code>cimagl</code>, declared in <code><complex.h></code> and also provided as
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built-in functions by GCC.
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</p>
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<a name="index-complex-conjugation"></a>
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<p>The operator ‘<samp>~</samp>’ performs complex conjugation when used on a value
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with a complex type. This is a GNU extension; for values of
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floating type, you should use the ISO C99 functions <code>conjf</code>,
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<code>conj</code> and <code>conjl</code>, declared in <code><complex.h></code> and also
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provided as built-in functions by GCC.
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</p>
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<p>GCC can allocate complex automatic variables in a noncontiguous
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fashion; it’s even possible for the real part to be in a register while
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the imaginary part is on the stack (or vice versa). Only the DWARF
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debug info format can represent this, so use of DWARF is recommended.
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If you are using the stabs debug info format, GCC describes a noncontiguous
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complex variable as if it were two separate variables of noncomplex type.
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If the variable’s actual name is <code>foo</code>, the two fictitious
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variables are named <code>foo$real</code> and <code>foo$imag</code>. You can
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examine and set these two fictitious variables with your debugger.
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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="Floating-Types.html#Floating-Types" accesskey="n" rel="next">Floating Types</a>, Previous: <a href="Long-Long.html#Long-Long" accesskey="p" rel="prev">Long Long</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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