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306 lines
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306 lines
13 KiB
HTML
4 years ago
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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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<head>
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<title>Character Sets (Debugging with GDB)</title>
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<meta name="description" content="Character Sets (Debugging with GDB)">
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<meta name="keywords" content="Character Sets (Debugging with GDB)">
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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="Data.html#Data" rel="up" title="Data">
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<link href="Caching-Target-Data.html#Caching-Target-Data" rel="next" title="Caching Target Data">
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</head>
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<body lang="en">
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<a name="Character-Sets"></a>
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<div class="header">
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<p>
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Next: <a href="Caching-Target-Data.html#Caching-Target-Data" accesskey="n" rel="next">Caching Target Data</a>, Previous: <a href="Core-File-Generation.html#Core-File-Generation" accesskey="p" rel="prev">Core File Generation</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>
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</div>
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<hr>
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<a name="Character-Sets-1"></a>
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<h3 class="section">10.20 Character Sets</h3>
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<a name="index-character-sets"></a>
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<a name="index-charset"></a>
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<a name="index-translating-between-character-sets"></a>
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<a name="index-host-character-set"></a>
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<a name="index-target-character-set"></a>
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<p>If the program you are debugging uses a different character set to
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represent characters and strings than the one <small>GDB</small> uses itself,
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<small>GDB</small> can automatically translate between the character sets for
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you. The character set <small>GDB</small> uses we call the <em>host
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character set</em>; the one the inferior program uses we call the
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<em>target character set</em>.
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</p>
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<p>For example, if you are running <small>GDB</small> on a <small>GNU</small>/Linux system, which
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uses the ISO Latin 1 character set, but you are using <small>GDB</small>’s
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remote protocol (see <a href="Remote-Debugging.html#Remote-Debugging">Remote Debugging</a>) to debug a program
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running on an IBM mainframe, which uses the <small>EBCDIC</small> character set,
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then the host character set is Latin-1, and the target character set is
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<small>EBCDIC</small>. If you give <small>GDB</small> the command <code>set
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target-charset EBCDIC-US</code>, then <small>GDB</small> translates between
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<small>EBCDIC</small> and Latin 1 as you print character or string values, or use
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character and string literals in expressions.
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</p>
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<p><small>GDB</small> has no way to automatically recognize which character set
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the inferior program uses; you must tell it, using the <code>set
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target-charset</code> command, described below.
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</p>
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<p>Here are the commands for controlling <small>GDB</small>’s character set
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support:
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</p>
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<dl compact="compact">
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<dt><code>set target-charset <var>charset</var></code></dt>
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<dd><a name="index-set-target_002dcharset"></a>
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<p>Set the current target character set to <var>charset</var>. To display the
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list of supported target character sets, type
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<kbd>set <span class="nolinebreak">target-charset</span> <span class="key">TAB</span><span class="key">TAB</span><!-- /@w --></kbd>.
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</p>
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</dd>
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<dt><code>set host-charset <var>charset</var></code></dt>
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<dd><a name="index-set-host_002dcharset"></a>
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<p>Set the current host character set to <var>charset</var>.
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</p>
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<p>By default, <small>GDB</small> uses a host character set appropriate to the
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system it is running on; you can override that default using the
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<code>set host-charset</code> command. On some systems, <small>GDB</small> cannot
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automatically determine the appropriate host character set. In this
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case, <small>GDB</small> uses ‘<samp>UTF-8</samp>’.
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</p>
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<p><small>GDB</small> can only use certain character sets as its host character
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set. If you type <kbd>set <span class="nolinebreak">host-charset</span> <span class="key">TAB</span><span class="key">TAB</span><!-- /@w --></kbd>,
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<small>GDB</small> will list the host character sets it supports.
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</p>
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</dd>
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<dt><code>set charset <var>charset</var></code></dt>
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<dd><a name="index-set-charset"></a>
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<p>Set the current host and target character sets to <var>charset</var>. As
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above, if you type <kbd>set charset <span class="key">TAB</span><span class="key">TAB</span><!-- /@w --></kbd>,
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<small>GDB</small> will list the names of the character sets that can be used
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for both host and target.
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</p>
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</dd>
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<dt><code>show charset</code></dt>
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<dd><a name="index-show-charset"></a>
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<p>Show the names of the current host and target character sets.
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</p>
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</dd>
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<dt><code>show host-charset</code></dt>
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<dd><a name="index-show-host_002dcharset"></a>
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<p>Show the name of the current host character set.
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</p>
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</dd>
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<dt><code>show target-charset</code></dt>
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<dd><a name="index-show-target_002dcharset"></a>
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<p>Show the name of the current target character set.
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</p>
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</dd>
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<dt><code>set target-wide-charset <var>charset</var></code></dt>
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<dd><a name="index-set-target_002dwide_002dcharset"></a>
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<p>Set the current target’s wide character set to <var>charset</var>. This is
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the character set used by the target’s <code>wchar_t</code> type. To
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display the list of supported wide character sets, type
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<kbd>set <span class="nolinebreak">target-wide-charset</span> <span class="key">TAB</span><span class="key">TAB</span><!-- /@w --></kbd>.
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</p>
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</dd>
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<dt><code>show target-wide-charset</code></dt>
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<dd><a name="index-show-target_002dwide_002dcharset"></a>
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<p>Show the name of the current target’s wide character set.
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</p></dd>
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</dl>
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<p>Here is an example of <small>GDB</small>’s character set support in action.
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Assume that the following source code has been placed in the file
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<samp>charset-test.c</samp>:
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</p>
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<div class="smallexample">
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<pre class="smallexample">#include <stdio.h>
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char ascii_hello[]
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= {72, 101, 108, 108, 111, 44, 32, 119,
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111, 114, 108, 100, 33, 10, 0};
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char ibm1047_hello[]
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= {200, 133, 147, 147, 150, 107, 64, 166,
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150, 153, 147, 132, 90, 37, 0};
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main ()
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{
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printf ("Hello, world!\n");
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}
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</pre></div>
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<p>In this program, <code>ascii_hello</code> and <code>ibm1047_hello</code> are arrays
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containing the string ‘<samp>Hello, world!</samp>’ followed by a newline,
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encoded in the <small>ASCII</small> and <small>IBM1047</small> character sets.
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</p>
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<p>We compile the program, and invoke the debugger on it:
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</p>
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<div class="smallexample">
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<pre class="smallexample">$ gcc -g charset-test.c -o charset-test
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$ gdb -nw charset-test
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GNU gdb 2001-12-19-cvs
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Copyright 2001 Free Software Foundation, Inc.
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…
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(gdb)
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</pre></div>
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<p>We can use the <code>show charset</code> command to see what character sets
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<small>GDB</small> is currently using to interpret and display characters and
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strings:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) show charset
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The current host and target character set is `ISO-8859-1'.
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(gdb)
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</pre></div>
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<p>For the sake of printing this manual, let’s use <small>ASCII</small> as our
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initial character set:
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</p><div class="smallexample">
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<pre class="smallexample">(gdb) set charset ASCII
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(gdb) show charset
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The current host and target character set is `ASCII'.
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(gdb)
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</pre></div>
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<p>Let’s assume that <small>ASCII</small> is indeed the correct character set for our
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host system — in other words, let’s assume that if <small>GDB</small> prints
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characters using the <small>ASCII</small> character set, our terminal will display
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them properly. Since our current target character set is also
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<small>ASCII</small>, the contents of <code>ascii_hello</code> print legibly:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print ascii_hello
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$1 = 0x401698 "Hello, world!\n"
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(gdb) print ascii_hello[0]
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$2 = 72 'H'
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(gdb)
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</pre></div>
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<p><small>GDB</small> uses the target character set for character and string
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literals you use in expressions:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print '+'
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$3 = 43 '+'
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(gdb)
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</pre></div>
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<p>The <small>ASCII</small> character set uses the number 43 to encode the ‘<samp>+</samp>’
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character.
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</p>
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<p><small>GDB</small> relies on the user to tell it which character set the
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target program uses. If we print <code>ibm1047_hello</code> while our target
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character set is still <small>ASCII</small>, we get jibberish:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print ibm1047_hello
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$4 = 0x4016a8 "\310\205\223\223\226k@\246\226\231\223\204Z%"
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(gdb) print ibm1047_hello[0]
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$5 = 200 '\310'
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(gdb)
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</pre></div>
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<p>If we invoke the <code>set target-charset</code> followed by <tt class="key">TAB</tt><tt class="key">TAB</tt>,
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<small>GDB</small> tells us the character sets it supports:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) set target-charset
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ASCII EBCDIC-US IBM1047 ISO-8859-1
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(gdb) set target-charset
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</pre></div>
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<p>We can select <small>IBM1047</small> as our target character set, and examine the
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program’s strings again. Now the <small>ASCII</small> string is wrong, but
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<small>GDB</small> translates the contents of <code>ibm1047_hello</code> from the
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target character set, <small>IBM1047</small>, to the host character set,
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<small>ASCII</small>, and they display correctly:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) set target-charset IBM1047
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(gdb) show charset
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The current host character set is `ASCII'.
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The current target character set is `IBM1047'.
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(gdb) print ascii_hello
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$6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
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(gdb) print ascii_hello[0]
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$7 = 72 '\110'
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(gdb) print ibm1047_hello
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$8 = 0x4016a8 "Hello, world!\n"
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(gdb) print ibm1047_hello[0]
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$9 = 200 'H'
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(gdb)
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</pre></div>
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<p>As above, <small>GDB</small> uses the target character set for character and
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string literals you use in expressions:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print '+'
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$10 = 78 '+'
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(gdb)
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</pre></div>
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<p>The <small>IBM1047</small> character set uses the number 78 to encode the ‘<samp>+</samp>’
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character.
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</p>
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<hr>
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<div class="header">
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||
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<p>
|
||
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Next: <a href="Caching-Target-Data.html#Caching-Target-Data" accesskey="n" rel="next">Caching Target Data</a>, Previous: <a href="Core-File-Generation.html#Core-File-Generation" accesskey="p" rel="prev">Core File Generation</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>
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||
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</div>
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</body>
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</html>
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