You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
139 lines
6.2 KiB
HTML
139 lines
6.2 KiB
HTML
4 years ago
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- 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." -->
|
||
|
|
<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>Expressions (Debugging with GDB)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Expressions (Debugging with GDB)">
|
||
|
|
<meta name="keywords" content="Expressions (Debugging with GDB)">
|
||
|
|
<meta name="resource-type" content="document">
|
||
|
|
<meta name="distribution" content="global">
|
||
|
|
<meta name="Generator" content="makeinfo">
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
||
|
|
<link href="index.html#Top" rel="start" title="Top">
|
||
|
|
<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="Data.html#Data" rel="up" title="Data">
|
||
|
|
<link href="Ambiguous-Expressions.html#Ambiguous-Expressions" rel="next" title="Ambiguous Expressions">
|
||
|
|
<link href="Data.html#Data" rel="prev" title="Data">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.indentedblock {margin-right: 0em}
|
||
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
||
|
|
blockquote.smallquotation {font-size: smaller}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
div.smalldisplay {margin-left: 3.2em}
|
||
|
|
div.smallexample {margin-left: 3.2em}
|
||
|
|
div.smalllisp {margin-left: 3.2em}
|
||
|
|
kbd {font-style: oblique}
|
||
|
|
pre.display {font-family: inherit}
|
||
|
|
pre.format {font-family: inherit}
|
||
|
|
pre.menu-comment {font-family: serif}
|
||
|
|
pre.menu-preformatted {font-family: serif}
|
||
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
||
|
|
pre.smallexample {font-size: smaller}
|
||
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
||
|
|
pre.smalllisp {font-size: smaller}
|
||
|
|
span.nolinebreak {white-space: nowrap}
|
||
|
|
span.roman {font-family: initial; font-weight: normal}
|
||
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<a name="Expressions"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Ambiguous-Expressions.html#Ambiguous-Expressions" accesskey="n" rel="next">Ambiguous Expressions</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</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>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<a name="Expressions-1"></a>
|
||
|
|
<h3 class="section">10.1 Expressions</h3>
|
||
|
|
|
||
|
|
<a name="index-expressions"></a>
|
||
|
|
<p><code>print</code> and many other <small>GDB</small> commands accept an expression and
|
||
|
|
compute its value. Any kind of constant, variable or operator defined
|
||
|
|
by the programming language you are using is valid in an expression in
|
||
|
|
<small>GDB</small>. This includes conditional expressions, function calls,
|
||
|
|
casts, and string constants. It also includes preprocessor macros, if
|
||
|
|
you compiled your program to include this information; see
|
||
|
|
<a href="Compilation.html#Compilation">Compilation</a>.
|
||
|
|
</p>
|
||
|
|
<a name="index-arrays-in-expressions"></a>
|
||
|
|
<p><small>GDB</small> supports array constants in expressions input by
|
||
|
|
the user. The syntax is {<var>element</var>, <var>element</var>…}. For example,
|
||
|
|
you can use the command <code>print {1, 2, 3}</code> to create an array
|
||
|
|
of three integers. If you pass an array to a function or assign it
|
||
|
|
to a program variable, <small>GDB</small> copies the array to memory that
|
||
|
|
is <code>malloc</code>ed in the target program.
|
||
|
|
</p>
|
||
|
|
<p>Because C is so widespread, most of the expressions shown in examples in
|
||
|
|
this manual are in C. See <a href="Languages.html#Languages">Using <small>GDB</small> with Different
|
||
|
|
Languages</a>, for information on how to use expressions in other
|
||
|
|
languages.
|
||
|
|
</p>
|
||
|
|
<p>In this section, we discuss operators that you can use in <small>GDB</small>
|
||
|
|
expressions regardless of your programming language.
|
||
|
|
</p>
|
||
|
|
<a name="index-casts_002c-in-expressions"></a>
|
||
|
|
<p>Casts are supported in all languages, not just in C, because it is so
|
||
|
|
useful to cast a number into a pointer in order to examine a structure
|
||
|
|
at that address in memory.
|
||
|
|
</p>
|
||
|
|
<p><small>GDB</small> supports these operators, in addition to those common
|
||
|
|
to programming languages:
|
||
|
|
</p>
|
||
|
|
<dl compact="compact">
|
||
|
|
<dt><code>@</code></dt>
|
||
|
|
<dd><p>‘<samp>@</samp>’ is a binary operator for treating parts of memory as arrays.
|
||
|
|
See <a href="Arrays.html#Arrays">Artificial Arrays</a>, for more information.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
<dt><code>::</code></dt>
|
||
|
|
<dd><p>‘<samp>::</samp>’ allows you to specify a variable in terms of the file or
|
||
|
|
function where it is defined. See <a href="Variables.html#Variables">Program Variables</a>.
|
||
|
|
</p>
|
||
|
|
<a name="index-_007btype_007d"></a>
|
||
|
|
<a name="index-type-casting-memory"></a>
|
||
|
|
<a name="index-memory_002c-viewing-as-typed-object"></a>
|
||
|
|
<a name="index-casts_002c-to-view-memory"></a>
|
||
|
|
</dd>
|
||
|
|
<dt><code>{<var>type</var>} <var>addr</var></code></dt>
|
||
|
|
<dd><p>Refers to an object of type <var>type</var> stored at address <var>addr</var> in
|
||
|
|
memory. The address <var>addr</var> may be any expression whose value is
|
||
|
|
an integer or pointer (but parentheses are required around binary
|
||
|
|
operators, just as in a cast). This construct is allowed regardless
|
||
|
|
of what kind of data is normally supposed to reside at <var>addr</var>.
|
||
|
|
</p></dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Ambiguous-Expressions.html#Ambiguous-Expressions" accesskey="n" rel="next">Ambiguous Expressions</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</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>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|