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107 lines
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107 lines
5.7 KiB
HTML
4 years ago
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<title>Complex - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions">
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<link rel="prev" href="Long-Long.html#Long-Long" title="Long Long">
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<link rel="next" href="Floating-Types.html#Floating-Types" title="Floating Types">
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Copyright (C) 1988-2015 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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<body>
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<div class="node">
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<a name="Complex"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Floating-Types.html#Floating-Types">Floating Types</a>,
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Previous: <a rel="previous" accesskey="p" href="Long-Long.html#Long-Long">Long Long</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<hr>
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</div>
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<h3 class="section">6.10 Complex Numbers</h3>
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<p><a name="index-complex-numbers-2910"></a><a name="index-g_t_0040code_007b_005fComplex_007d-keyword-2911"></a><a name="index-g_t_0040code_007b_005f_005fcomplex_005f_005f_007d-keyword-2912"></a>
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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>For example, ‘<samp><span class="samp">_Complex double x;</span></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><span class="samp">_Complex short int y;</span></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>To write a constant with a complex data type, use the suffix ‘<samp><span class="samp">i</span></samp>’ or
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‘<samp><span class="samp">j</span></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><a name="index-g_t_0040code_007b_005f_005freal_005f_005f_007d-keyword-2913"></a><a name="index-g_t_0040code_007b_005f_005fimag_005f_005f_007d-keyword-2914"></a>To extract the real part of a complex-valued expression <var>exp</var>, write
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<code>__real__ </code><var>exp</var>. 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><a name="index-complex-conjugation-2915"></a>The operator ‘<samp><span class="samp">~</span></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>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 2
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debug info format can represent this, so use of DWARF 2 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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</body></html>
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