<html lang="en">
<head>
<title>Complex - Using the GNU Compiler Collection (GCC)</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Using the GNU Compiler Collection (GCC)">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions">
<link rel="prev" href="Long-Long.html#Long-Long" title="Long Long">
<link rel="next" href="Floating-Types.html#Floating-Types" title="Floating Types">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1988-2015 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.-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
pre.display { font-family:inherit }
pre.format { font-family:inherit }
pre.smalldisplay { font-family:inherit; font-size:smaller }
pre.smallformat { font-family:inherit; font-size:smaller }
pre.smallexample { font-size:smaller }
pre.smalllisp { font-size:smaller }
span.sc { font-variant:small-caps }
span.roman { font-family:serif; font-weight:normal; }
span.sansserif { font-family:sans-serif; font-weight:normal; }
--></style>
</head>
<body>
<div class="node">
<a name="Complex"></a>
<p>
Next: <a rel="next" accesskey="n" href="Floating-Types.html#Floating-Types">Floating Types</a>,
Previous: <a rel="previous" accesskey="p" href="Long-Long.html#Long-Long">Long Long</a>,
Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
<hr>
</div>
<h3 class="section">6.10 Complex Numbers</h3>
<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>
ISO C99 supports complex floating data types, and as an extension GCC
supports them in C90 mode and in C++. GCC also supports complex integer data
types which are not part of ISO C99. You can declare complex types
using the keyword <code>_Complex</code>. As an extension, the older GNU
keyword <code>__complex__</code> is also supported.
<p>For example, ‘<samp><span class="samp">_Complex double x;</span></samp>’ declares <code>x</code> as a
variable whose real part and imaginary part are both of type
<code>double</code>. ‘<samp><span class="samp">_Complex short int y;</span></samp>’ declares <code>y</code> to
have real and imaginary parts of type <code>short int</code>; this is not
likely to be useful, but it shows that the set of complex types is
complete.
<p>To write a constant with a complex data type, use the suffix ‘<samp><span class="samp">i</span></samp>’ or
‘<samp><span class="samp">j</span></samp>’ (either one; they are equivalent). For example, <code>2.5fi</code>
has type <code>_Complex float</code> and <code>3i</code> has type
<code>_Complex int</code>. Such a constant always has a pure imaginary
value, but you can form any complex value you like by adding one to a
real constant. This is a GNU extension; if you have an ISO C99
conforming C library (such as the GNU C Library), and want to construct complex
constants of floating type, you should include <code><complex.h></code> and
use the macros <code>I</code> or <code>_Complex_I</code> instead.
<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
<code>__real__ </code><var>exp</var>. Likewise, use <code>__imag__</code> to
extract the imaginary part. This is a GNU extension; for values of
floating type, you should use the ISO C99 functions <code>crealf</code>,
<code>creal</code>, <code>creall</code>, <code>cimagf</code>, <code>cimag</code> and
<code>cimagl</code>, declared in <code><complex.h></code> and also provided as
built-in functions by GCC.
<p><a name="index-complex-conjugation-2915"></a>The operator ‘<samp><span class="samp">~</span></samp>’ performs complex conjugation when used on a value
with a complex type. This is a GNU extension; for values of
floating type, you should use the ISO C99 functions <code>conjf</code>,
<code>conj</code> and <code>conjl</code>, declared in <code><complex.h></code> and also
provided as built-in functions by GCC.
<p>GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice versa). Only the DWARF 2
debug info format can represent this, so use of DWARF 2 is recommended.
If you are using the stabs debug info format, GCC describes a noncontiguous
complex variable as if it were two separate variables of noncomplex type.
If the variable's actual name is <code>foo</code>, the two fictitious
variables are named <code>foo$real</code> and <code>foo$imag</code>. You can
examine and set these two fictitious variables with your debugger.
</body></html>