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256 lines
9.8 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) 1988-2019 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 "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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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>C Operators (Debugging with GDB)</title>
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<meta name="description" content="C Operators (Debugging with GDB)">
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<meta name="keywords" content="C Operators (Debugging with GDB)">
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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="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C.html#C" rel="up" title="C">
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<link href="C-Constants.html#C-Constants" rel="next" title="C Constants">
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<link href="C.html#C" rel="prev" title="C">
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</head>
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<body lang="en">
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<a name="C-Operators"></a>
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<div class="header">
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<p>
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Next: <a href="C-Constants.html#C-Constants" accesskey="n" rel="next">C Constants</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="C-and-C_002b_002b-Operators"></a>
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<h4 class="subsubsection">15.4.1.1 C and C<tt>++</tt> Operators</h4>
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<a name="index-C-and-C_002b_002b-operators"></a>
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<p>Operators must be defined on values of specific types. For instance,
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<code>+</code> is defined on numbers, but not on structures. Operators are
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often defined on groups of types.
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</p>
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<p>For the purposes of C and C<tt>++</tt>, the following definitions hold:
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</p>
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<ul>
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<li> <em>Integral types</em> include <code>int</code> with any of its storage-class
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specifiers; <code>char</code>; <code>enum</code>; and, for C<tt>++</tt>, <code>bool</code>.
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</li><li> <em>Floating-point types</em> include <code>float</code>, <code>double</code>, and
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<code>long double</code> (if supported by the target platform).
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</li><li> <em>Pointer types</em> include all types defined as <code>(<var>type</var> *)</code>.
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</li><li> <em>Scalar types</em> include all of the above.
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</li></ul>
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<p>The following operators are supported. They are listed here
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in order of increasing precedence:
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</p>
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<dl compact="compact">
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<dt><code>,</code></dt>
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<dd><p>The comma or sequencing operator. Expressions in a comma-separated list
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are evaluated from left to right, with the result of the entire
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expression being the last expression evaluated.
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</p>
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</dd>
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<dt><code>=</code></dt>
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<dd><p>Assignment. The value of an assignment expression is the value
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assigned. Defined on scalar types.
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</p>
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</dd>
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<dt><code><var>op</var>=</code></dt>
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<dd><p>Used in an expression of the form <code><var>a</var> <var>op</var>= <var>b</var></code><!-- /@w -->,
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and translated to <code><var>a</var> = <var>a op b</var></code><!-- /@w -->.
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<code><var>op</var>=</code><!-- /@w --> and <code>=</code> have the same precedence. The operator
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<var>op</var> is any one of the operators <code>|</code>, <code>^</code>, <code>&</code>,
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<code><<</code>, <code>>></code>, <code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>, <code>%</code>.
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</p>
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</dd>
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<dt><code>?:</code></dt>
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<dd><p>The ternary operator. <code><var>a</var> ? <var>b</var> : <var>c</var></code> can be thought
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of as: if <var>a</var> then <var>b</var> else <var>c</var>. The argument <var>a</var>
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should be of an integral type.
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</p>
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</dd>
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<dt><code>||</code></dt>
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<dd><p>Logical <small>OR</small>. Defined on integral types.
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</p>
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</dd>
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<dt><code>&&</code></dt>
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<dd><p>Logical <small>AND</small>. Defined on integral types.
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</p>
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</dd>
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<dt><code>|</code></dt>
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<dd><p>Bitwise <small>OR</small>. Defined on integral types.
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</p>
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</dd>
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<dt><code>^</code></dt>
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<dd><p>Bitwise exclusive-<small>OR</small>. Defined on integral types.
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</p>
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</dd>
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<dt><code>&</code></dt>
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<dd><p>Bitwise <small>AND</small>. Defined on integral types.
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</p>
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</dd>
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<dt><code>==<span class="roman">, </span>!=</code></dt>
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<dd><p>Equality and inequality. Defined on scalar types. The value of these
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expressions is 0 for false and non-zero for true.
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</p>
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</dd>
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<dt><code><<span class="roman">, </span>><span class="roman">, </span><=<span class="roman">, </span>>=</code></dt>
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<dd><p>Less than, greater than, less than or equal, greater than or equal.
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Defined on scalar types. The value of these expressions is 0 for false
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and non-zero for true.
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</p>
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</dd>
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<dt><code><<<span class="roman">, </span>>></code></dt>
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<dd><p>left shift, and right shift. Defined on integral types.
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</p>
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</dd>
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<dt><code>@</code></dt>
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<dd><p>The <small>GDB</small> “artificial array” operator (see <a href="Expressions.html#Expressions">Expressions</a>).
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</p>
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</dd>
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<dt><code>+<span class="roman">, </span>-</code></dt>
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<dd><p>Addition and subtraction. Defined on integral types, floating-point types and
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pointer types.
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</p>
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</dd>
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<dt><code>*<span class="roman">, </span>/<span class="roman">, </span>%</code></dt>
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<dd><p>Multiplication, division, and modulus. Multiplication and division are
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defined on integral and floating-point types. Modulus is defined on
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integral types.
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</p>
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</dd>
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<dt><code>++<span class="roman">, </span>--</code></dt>
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<dd><p>Increment and decrement. When appearing before a variable, the
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operation is performed before the variable is used in an expression;
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when appearing after it, the variable’s value is used before the
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operation takes place.
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</p>
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</dd>
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<dt><code>*</code></dt>
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<dd><p>Pointer dereferencing. Defined on pointer types. Same precedence as
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<code>++</code>.
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</p>
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</dd>
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<dt><code>&</code></dt>
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<dd><p>Address operator. Defined on variables. Same precedence as <code>++</code>.
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</p>
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<p>For debugging C<tt>++</tt>, <small>GDB</small> implements a use of ‘<samp>&</samp>’ beyond what is
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allowed in the C<tt>++</tt> language itself: you can use ‘<samp>&(&<var>ref</var>)</samp>’
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to examine the address
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where a C<tt>++</tt> reference variable (declared with ‘<samp>&<var>ref</var></samp>’) is
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stored.
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</p>
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</dd>
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<dt><code>-</code></dt>
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<dd><p>Negative. Defined on integral and floating-point types. Same
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precedence as <code>++</code>.
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</p>
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</dd>
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<dt><code>!</code></dt>
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<dd><p>Logical negation. Defined on integral types. Same precedence as
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<code>++</code>.
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</p>
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</dd>
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<dt><code>~</code></dt>
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<dd><p>Bitwise complement operator. Defined on integral types. Same precedence as
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<code>++</code>.
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</p>
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</dd>
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<dt><code>.<span class="roman">, </span>-></code></dt>
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<dd><p>Structure member, and pointer-to-structure member. For convenience,
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<small>GDB</small> regards the two as equivalent, choosing whether to dereference a
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pointer based on the stored type information.
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Defined on <code>struct</code> and <code>union</code> data.
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</p>
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</dd>
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<dt><code>.*<span class="roman">, </span>->*</code></dt>
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<dd><p>Dereferences of pointers to members.
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</p>
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</dd>
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<dt><code>[]</code></dt>
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<dd><p>Array indexing. <code><var>a</var>[<var>i</var>]</code> is defined as
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<code>*(<var>a</var>+<var>i</var>)</code>. Same precedence as <code>-></code>.
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</p>
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</dd>
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<dt><code>()</code></dt>
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<dd><p>Function parameter list. Same precedence as <code>-></code>.
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</p>
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</dd>
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<dt><code>::</code></dt>
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<dd><p>C<tt>++</tt> scope resolution operator. Defined on <code>struct</code>, <code>union</code>,
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and <code>class</code> types.
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</p>
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</dd>
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<dt><code>::</code></dt>
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<dd><p>Doubled colons also represent the <small>GDB</small> scope operator
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(see <a href="Expressions.html#Expressions">Expressions</a>). Same precedence as <code>::</code>,
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above.
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</p></dd>
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</dl>
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<p>If an operator is redefined in the user code, <small>GDB</small> usually
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attempts to invoke the redefined version instead of using the operator’s
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predefined meaning.
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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="C-Constants.html#C-Constants" accesskey="n" rel="next">C Constants</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-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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