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<html lang="en"><head><title>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 4.6"><!--Copyright © 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc. <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below). A copy of the license isincluded in the section entitled "GNU Free Documentation License". <p>(a) The FSF's Front-Cover Text is: <p>A GNU Manual <p>(b) The FSF's Back-Cover Text is: <p>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 }--></style></head><body><div class="node"><p>Node: <a name="Complex">Complex</a>,Next: <a rel="next" accesskey="n" href="Hex-Floats.html#Hex%20Floats">Hex Floats</a>,Previous: <a rel="previous" accesskey="p" href="Long-Long.html#Long%20Long">Long Long</a>,Up: <a rel="up" accesskey="u" href="C-Extensions.html#C%20Extensions">C Extensions</a><hr><br></div><h3 class="section">Complex Numbers</h3><p>ISO C99 supports complex floating data types, and as an extension GCCsupports them in C89 mode and in C++, and supports complex integer datatypes which are not part of ISO C99. You can declare complex typesusing the keyword <code>_Complex</code>. As an extension, the older GNUkeyword <code>__complex__</code> is also supported. <p>For example, <code>_Complex double x;</code> declares <code>x</code> as avariable whose real part and imaginary part are both of type<code>double</code>. <code>_Complex short int y;</code> declares <code>y</code> tohave real and imaginary parts of type <code>short int</code>; this is notlikely to be useful, but it shows that the set of complex types iscomplete. <p>To write a constant with a complex data type, use the suffix <code>i</code> or<code>j</code> (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 imaginaryvalue, but you can form any complex value you like by adding one to areal constant. This is a GNU extension; if you have an ISO C99conforming C library (such as GNU libc), and want to construct complexconstants of floating type, you should include <code><complex.h></code> anduse the macros <code>I</code> or <code>_Complex_I</code> instead. <p>To extract the real part of a complex-valued expression <var>exp</var>, write<code>__real__ </code><var>exp</var><code></code>. Likewise, use <code>__imag__</code> toextract the imaginary part. This is a GNU extension; for values offloating 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 asbuilt-in functions by GCC. <p>The operator <code>~</code> performs complex conjugation when used on a valuewith a complex type. This is a GNU extension; for values offloating 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 alsoprovided as built-in functions by GCC. <p>GCC can allocate complex automatic variables in a noncontiguousfashion; it's even possible for the real part to be in a register whilethe imaginary part is on the stack (or vice-versa). Only the DWARF2debug info format can represent this, so use of DWARF2 is recommended. If you are using the stabs debug info format, GCC describes a noncontiguouscomplex variable as if it were two separate variables of noncomplex type. If the variable's actual name is <code>foo</code>, the two fictitiousvariables are named <code>foo$real</code> and <code>foo$imag</code>. You canexamine and set these two fictitious variables with your debugger. </body></html>⌨️ 快捷键说明
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