169 lines
8.5 KiB
HTML
169 lines
8.5 KiB
HTML
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>C Operators - Debugging with GDB</title>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<meta name="description" content="Debugging with GDB">
|
||
|
|
<meta name="generator" content="makeinfo 4.13">
|
||
|
|
<link title="Top" rel="start" href="index.html#Top">
|
||
|
|
<link rel="up" href="C.html#C" title="C">
|
||
|
|
<link rel="next" href="C-Constants.html#C-Constants" title="C Constants">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
Copyright (C) 1988-2019 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 ``Free Software'' and ``Free Software Needs
|
||
|
|
Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
|
||
|
|
and with the Back-Cover Texts as in (a) below.
|
||
|
|
|
||
|
|
(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
|
||
|
|
this GNU Manual. Buying copies from GNU Press supports the FSF in
|
||
|
|
developing GNU and promoting software freedom.''
|
||
|
|
-->
|
||
|
|
<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="C-Operators"></a>
|
||
|
|
<p>
|
||
|
|
Next: <a rel="next" accesskey="n" href="C-Constants.html#C-Constants">C Constants</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="C.html#C">C</a>
|
||
|
|
<hr>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h5 class="subsubsection">15.4.1.1 C and C<tt>++</tt> Operators</h5>
|
||
|
|
|
||
|
|
<p><a name="index-C-and-C_0040t_007b_002b_002b_007d-operators-986"></a>
|
||
|
|
Operators must be defined on values of specific types. For instance,
|
||
|
|
<code>+</code> is defined on numbers, but not on structures. Operators are
|
||
|
|
often defined on groups of types.
|
||
|
|
|
||
|
|
<p>For the purposes of C and C<tt>++</tt>, the following definitions hold:
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li><em>Integral types</em> include <code>int</code> with any of its storage-class
|
||
|
|
specifiers; <code>char</code>; <code>enum</code>; and, for C<tt>++</tt>, <code>bool</code>.
|
||
|
|
|
||
|
|
<li><em>Floating-point types</em> include <code>float</code>, <code>double</code>, and
|
||
|
|
<code>long double</code> (if supported by the target platform).
|
||
|
|
|
||
|
|
<li><em>Pointer types</em> include all types defined as <code>(</code><var>type</var><code> *)</code>.
|
||
|
|
|
||
|
|
<li><em>Scalar types</em> include all of the above.
|
||
|
|
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<p class="noindent">The following operators are supported. They are listed here
|
||
|
|
in order of increasing precedence:
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><code>,</code><dd>The comma or sequencing operator. Expressions in a comma-separated list
|
||
|
|
are evaluated from left to right, with the result of the entire
|
||
|
|
expression being the last expression evaluated.
|
||
|
|
|
||
|
|
<br><dt><code>=</code><dd>Assignment. The value of an assignment expression is the value
|
||
|
|
assigned. Defined on scalar types.
|
||
|
|
|
||
|
|
<br><dt><var>op</var><code>=</code><dd>Used in an expression of the form <var>a</var><code> </code><var>op</var><code>= </code><var>b</var><!-- /@w -->,
|
||
|
|
and translated to <var>a</var><code> = </code><var>a op b</var><!-- /@w -->.
|
||
|
|
<var>op</var><code>=</code><!-- /@w --> and <code>=</code> have the same precedence. The operator
|
||
|
|
<var>op</var> is any one of the operators <code>|</code>, <code>^</code>, <code>&</code>,
|
||
|
|
<code><<</code>, <code>>></code>, <code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>, <code>%</code>.
|
||
|
|
|
||
|
|
<br><dt><code>?:</code><dd>The ternary operator. <var>a</var><code> ? </code><var>b</var><code> : </code><var>c</var> can be thought
|
||
|
|
of as: if <var>a</var> then <var>b</var> else <var>c</var>. The argument <var>a</var>
|
||
|
|
should be of an integral type.
|
||
|
|
|
||
|
|
<br><dt><code>||</code><dd>Logical <span class="sc">or</span>. Defined on integral types.
|
||
|
|
|
||
|
|
<br><dt><code>&&</code><dd>Logical <span class="sc">and</span>. Defined on integral types.
|
||
|
|
|
||
|
|
<br><dt><code>|</code><dd>Bitwise <span class="sc">or</span>. Defined on integral types.
|
||
|
|
|
||
|
|
<br><dt><code>^</code><dd>Bitwise exclusive-<span class="sc">or</span>. Defined on integral types.
|
||
|
|
|
||
|
|
<br><dt><code>&</code><dd>Bitwise <span class="sc">and</span>. Defined on integral types.
|
||
|
|
|
||
|
|
<br><dt><code>==</code><span class="roman">, </span><code>!=</code><dd>Equality and inequality. Defined on scalar types. The value of these
|
||
|
|
expressions is 0 for false and non-zero for true.
|
||
|
|
|
||
|
|
<br><dt><code><</code><span class="roman">, </span><code>></code><span class="roman">, </span><code><=</code><span class="roman">, </span><code>>=</code><dd>Less than, greater than, less than or equal, greater than or equal.
|
||
|
|
Defined on scalar types. The value of these expressions is 0 for false
|
||
|
|
and non-zero for true.
|
||
|
|
|
||
|
|
<br><dt><code><<</code><span class="roman">, </span><code>>></code><dd>left shift, and right shift. Defined on integral types.
|
||
|
|
|
||
|
|
<br><dt><code>@</code><dd>The <span class="sc">gdb</span> “artificial array” operator (see <a href="Expressions.html#Expressions">Expressions</a>).
|
||
|
|
|
||
|
|
<br><dt><code>+</code><span class="roman">, </span><code>-</code><dd>Addition and subtraction. Defined on integral types, floating-point types and
|
||
|
|
pointer types.
|
||
|
|
|
||
|
|
<br><dt><code>*</code><span class="roman">, </span><code>/</code><span class="roman">, </span><code>%</code><dd>Multiplication, division, and modulus. Multiplication and division are
|
||
|
|
defined on integral and floating-point types. Modulus is defined on
|
||
|
|
integral types.
|
||
|
|
|
||
|
|
<br><dt><code>++</code><span class="roman">, </span><code>--</code><dd>Increment and decrement. When appearing before a variable, the
|
||
|
|
operation is performed before the variable is used in an expression;
|
||
|
|
when appearing after it, the variable's value is used before the
|
||
|
|
operation takes place.
|
||
|
|
|
||
|
|
<br><dt><code>*</code><dd>Pointer dereferencing. Defined on pointer types. Same precedence as
|
||
|
|
<code>++</code>.
|
||
|
|
|
||
|
|
<br><dt><code>&</code><dd>Address operator. Defined on variables. Same precedence as <code>++</code>.
|
||
|
|
|
||
|
|
<p>For debugging C<tt>++</tt>, <span class="sc">gdb</span> implements a use of ‘<samp><span class="samp">&</span></samp>’ beyond what is
|
||
|
|
allowed in the C<tt>++</tt> language itself: you can use ‘<samp><span class="samp">&(&</span><var>ref</var><span class="samp">)</span></samp>’
|
||
|
|
to examine the address
|
||
|
|
where a C<tt>++</tt> reference variable (declared with ‘<samp><span class="samp">&</span><var>ref</var></samp>’) is
|
||
|
|
stored.
|
||
|
|
|
||
|
|
<br><dt><code>-</code><dd>Negative. Defined on integral and floating-point types. Same
|
||
|
|
precedence as <code>++</code>.
|
||
|
|
|
||
|
|
<br><dt><code>!</code><dd>Logical negation. Defined on integral types. Same precedence as
|
||
|
|
<code>++</code>.
|
||
|
|
|
||
|
|
<br><dt><code>~</code><dd>Bitwise complement operator. Defined on integral types. Same precedence as
|
||
|
|
<code>++</code>.
|
||
|
|
|
||
|
|
<br><dt><code>.</code><span class="roman">, </span><code>-></code><dd>Structure member, and pointer-to-structure member. For convenience,
|
||
|
|
<span class="sc">gdb</span> regards the two as equivalent, choosing whether to dereference a
|
||
|
|
pointer based on the stored type information.
|
||
|
|
Defined on <code>struct</code> and <code>union</code> data.
|
||
|
|
|
||
|
|
<br><dt><code>.*</code><span class="roman">, </span><code>->*</code><dd>Dereferences of pointers to members.
|
||
|
|
|
||
|
|
<br><dt><code>[]</code><dd>Array indexing. <var>a</var><code>[</code><var>i</var><code>]</code> is defined as
|
||
|
|
<code>*(</code><var>a</var><code>+</code><var>i</var><code>)</code>. Same precedence as <code>-></code>.
|
||
|
|
|
||
|
|
<br><dt><code>()</code><dd>Function parameter list. Same precedence as <code>-></code>.
|
||
|
|
|
||
|
|
<br><dt><code>::</code><dd>C<tt>++</tt> scope resolution operator. Defined on <code>struct</code>, <code>union</code>,
|
||
|
|
and <code>class</code> types.
|
||
|
|
|
||
|
|
<br><dt><code>::</code><dd>Doubled colons also represent the <span class="sc">gdb</span> scope operator
|
||
|
|
(see <a href="Expressions.html#Expressions">Expressions</a>). Same precedence as <code>::</code>,
|
||
|
|
above.
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<p>If an operator is redefined in the user code, <span class="sc">gdb</span> usually
|
||
|
|
attempts to invoke the redefined version instead of using the operator's
|
||
|
|
predefined meaning.
|
||
|
|
|
||
|
|
</body></html>
|
||
|
|
|