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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | 6ce4ebed87858ecdd79a1091367c6e961055daa9 (patch) | |
| tree | 1c2a6a60531acf791531bbd9c8ac14c23ef8a66c /share/doc/gdb/Assignment.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gdb/Assignment.html b/share/doc/gdb/Assignment.html new file mode 100644 index 0000000..a1ca2ea --- /dev/null +++ b/share/doc/gdb/Assignment.html @@ -0,0 +1,177 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 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 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Debugging with GDB: Assignment</title> + +<meta name="description" content="Debugging with GDB: Assignment"> +<meta name="keywords" content="Debugging with GDB: Assignment"> +<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="Altering.html#Altering" rel="up" title="Altering"> +<link href="Jumping.html#Jumping" rel="next" title="Jumping"> +<link href="Altering.html#Altering" rel="previous" title="Altering"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +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.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Assignment"></a> +<div class="header"> +<p> +Next: <a href="Jumping.html#Jumping" accesskey="n" rel="next">Jumping</a>, Up: <a href="Altering.html#Altering" accesskey="u" rel="up">Altering</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="Assignment-to-Variables"></a> +<h3 class="section">17.1 Assignment to Variables</h3> + +<a name="index-assignment"></a> +<a name="index-setting-variables"></a> +<p>To alter the value of a variable, evaluate an assignment expression. +See <a href="Expressions.html#Expressions">Expressions</a>. For example, +</p> +<div class="smallexample"> +<pre class="smallexample">print x=4 +</pre></div> + +<p>stores the value 4 into the variable <code>x</code>, and then prints the +value of the assignment expression (which is 4). +See <a href="Languages.html#Languages">Using <small>GDB</small> with Different Languages</a>, for more +information on operators in supported languages. +</p> +<a name="index-set-variable"></a> +<a name="index-variables_002c-setting"></a> +<p>If you are not interested in seeing the value of the assignment, use the +<code>set</code> command instead of the <code>print</code> command. <code>set</code> is +really the same as <code>print</code> except that the expression’s value is +not printed and is not put in the value history (see <a href="Value-History.html#Value-History">Value History</a>). The expression is evaluated only for its effects. +</p> +<p>If the beginning of the argument string of the <code>set</code> command +appears identical to a <code>set</code> subcommand, use the <code>set +variable</code> command instead of just <code>set</code>. This command is identical +to <code>set</code> except for its lack of subcommands. For example, if your +program has a variable <code>width</code>, you get an error if you try to set +a new value with just ‘<samp>set width=13</samp>’, because <small>GDB</small> has the +command <code>set width</code>: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) whatis width +type = double +(gdb) p width +$4 = 13 +(gdb) set width=47 +Invalid syntax in expression. +</pre></div> + +<p>The invalid expression, of course, is ‘<samp>=47</samp>’. In +order to actually set the program’s variable <code>width</code>, use +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) set var width=47 +</pre></div> + +<p>Because the <code>set</code> command has many subcommands that can conflict +with the names of program variables, it is a good idea to use the +<code>set variable</code> command instead of just <code>set</code>. For example, if +your program has a variable <code>g</code>, you run into problems if you try +to set a new value with just ‘<samp>set g=4</samp>’, because <small>GDB</small> has +the command <code>set gnutarget</code>, abbreviated <code>set g</code>: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) whatis g +type = double +(gdb) p g +$1 = 1 +(gdb) set g=4 +(gdb) p g +$2 = 1 +(gdb) r +The program being debugged has been started already. +Start it from the beginning? (y or n) y +Starting program: /home/smith/cc_progs/a.out +"/home/smith/cc_progs/a.out": can't open to read symbols: + Invalid bfd target. +(gdb) show g +The current BFD target is "=4". +</pre></div> + +<p>The program variable <code>g</code> did not change, and you silently set the +<code>gnutarget</code> to an invalid value. In order to set the variable +<code>g</code>, use +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) set var g=4 +</pre></div> + +<p><small>GDB</small> allows more implicit conversions in assignments than C; you can +freely store an integer value into a pointer variable or vice versa, +and you can convert any structure to any other structure that is the +same length or shorter. +</p> +<p>To store values into arbitrary places in memory, use the ‘<samp>{…}</samp>’ +construct to generate a value of specified type at a specified address +(see <a href="Expressions.html#Expressions">Expressions</a>). For example, <code>{int}0x83040</code> refers +to memory location <code>0x83040</code> as an integer (which implies a certain size +and representation in memory), and +</p> +<div class="smallexample"> +<pre class="smallexample">set {int}0x83040 = 4 +</pre></div> + +<p>stores the value 4 into that memory location. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Jumping.html#Jumping" accesskey="n" rel="next">Jumping</a>, Up: <a href="Altering.html#Altering" accesskey="u" rel="up">Altering</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> |