174 lines
9.5 KiB
HTML
174 lines
9.5 KiB
HTML
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<html lang="en">
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<head>
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<title>Output - Debugging with GDB</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Debugging with GDB">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Sequences.html#Sequences" title="Sequences">
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<link rel="prev" href="Command-Files.html#Command-Files" title="Command Files">
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<link rel="next" href="Auto_002dloading-sequences.html#Auto_002dloading-sequences" title="Auto-loading sequences">
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<!--
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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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this GNU Manual. Buying copies from GNU Press supports the FSF in
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</head>
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<body>
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<div class="node">
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<a name="Output"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Auto_002dloading-sequences.html#Auto_002dloading-sequences">Auto-loading sequences</a>,
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Previous: <a rel="previous" accesskey="p" href="Command-Files.html#Command-Files">Command Files</a>,
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Up: <a rel="up" accesskey="u" href="Sequences.html#Sequences">Sequences</a>
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<hr>
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</div>
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<h4 class="subsection">23.1.4 Commands for Controlled Output</h4>
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<p>During the execution of a command file or a user-defined command, normal
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<span class="sc">gdb</span> output is suppressed; the only output that appears is what is
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explicitly printed by the commands in the definition. This section
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describes three commands useful for generating exactly the output you
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want.
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<a name="index-echo-1827"></a>
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<dl><dt><code>echo </code><var>text</var><dd><!-- I do not consider backslash-space a standard C escape sequence -->
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<!-- because it is not in ANSI. -->
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Print <var>text</var>. Nonprinting characters can be included in
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<var>text</var> using C escape sequences, such as ‘<samp><span class="samp">\n</span></samp>’ to print a
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newline. <strong>No newline is printed unless you specify one.</strong>
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In addition to the standard C escape sequences, a backslash followed
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by a space stands for a space. This is useful for displaying a
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string with spaces at the beginning or the end, since leading and
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trailing spaces are otherwise trimmed from all arguments.
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To print ‘<samp><span class="samp"> <!-- /@w -->and foo = <!-- /@w --></span></samp>’, use the command
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‘<samp><span class="samp">echo \ <!-- /@w -->and foo = \ <!-- /@w --></span></samp>’.
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<p>A backslash at the end of <var>text</var> can be used, as in C, to continue
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the command onto subsequent lines. For example,
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<pre class="smallexample"> echo This is some text\n\
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which is continued\n\
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onto several lines.\n
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</pre>
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<p>produces the same output as
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<pre class="smallexample"> echo This is some text\n
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echo which is continued\n
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echo onto several lines.\n
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</pre>
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<p><a name="index-output-1828"></a><br><dt><code>output </code><var>expression</var><dd>Print the value of <var>expression</var> and nothing but that value: no
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newlines, no ‘<samp><span class="samp">$</span><var>nn</var><span class="samp"> = </span></samp>’. The value is not entered in the
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value history either. See <a href="Expressions.html#Expressions">Expressions</a>, for more information
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on expressions.
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<br><dt><code>output/</code><var>fmt</var> <var>expression</var><dd>Print the value of <var>expression</var> in format <var>fmt</var>. You can use
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the same formats as for <code>print</code>. See <a href="Output-Formats.html#Output-Formats">Output Formats</a>, for more information.
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<p><a name="index-printf-1829"></a><br><dt><code>printf </code><var>template</var><code>, </code><var>expressions</var><code>...</code><dd>Print the values of one or more <var>expressions</var> under the control of
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the string <var>template</var>. To print several values, make
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<var>expressions</var> be a comma-separated list of individual expressions,
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which may be either numbers or pointers. Their values are printed as
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specified by <var>template</var>, exactly as a C program would do by
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executing the code below:
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<pre class="smallexample"> printf (<var>template</var>, <var>expressions</var>...);
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</pre>
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<p>As in <code>C</code> <code>printf</code>, ordinary characters in <var>template</var>
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are printed verbatim, while <dfn>conversion specification</dfn> introduced
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by the ‘<samp><span class="samp">%</span></samp>’ character cause subsequent <var>expressions</var> to be
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evaluated, their values converted and formatted according to type and
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style information encoded in the conversion specifications, and then
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printed.
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<p>For example, you can print two values in hex like this:
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<pre class="smallexample"> printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
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</pre>
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<p><code>printf</code> supports all the standard <code>C</code> conversion
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specifications, including the flags and modifiers between the ‘<samp><span class="samp">%</span></samp>’
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character and the conversion letter, with the following exceptions:
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<ul>
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<li>The argument-ordering modifiers, such as ‘<samp><span class="samp">2$</span></samp>’, are not supported.
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<li>The modifier ‘<samp><span class="samp">*</span></samp>’ is not supported for specifying precision or
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width.
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<li>The ‘<samp><span class="samp">'</span></samp>’ flag (for separation of digits into groups according to
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<code>LC_NUMERIC'</code>) is not supported.
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<li>The type modifiers ‘<samp><span class="samp">hh</span></samp>’, ‘<samp><span class="samp">j</span></samp>’, ‘<samp><span class="samp">t</span></samp>’, and ‘<samp><span class="samp">z</span></samp>’ are not
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supported.
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<li>The conversion letter ‘<samp><span class="samp">n</span></samp>’ (as in ‘<samp><span class="samp">%n</span></samp>’) is not supported.
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<li>The conversion letters ‘<samp><span class="samp">a</span></samp>’ and ‘<samp><span class="samp">A</span></samp>’ are not supported.
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</ul>
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<p class="noindent">Note that the ‘<samp><span class="samp">ll</span></samp>’ type modifier is supported only if the
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underlying <code>C</code> implementation used to build <span class="sc">gdb</span> supports
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the <code>long long int</code> type, and the ‘<samp><span class="samp">L</span></samp>’ type modifier is
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supported only if <code>long double</code> type is available.
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<p>As in <code>C</code>, <code>printf</code> supports simple backslash-escape
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sequences, such as <code>\n</code>, ‘<samp><span class="samp">\t</span></samp>’, ‘<samp><span class="samp">\\</span></samp>’, ‘<samp><span class="samp">\"</span></samp>’,
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‘<samp><span class="samp">\a</span></samp>’, and ‘<samp><span class="samp">\f</span></samp>’, that consist of backslash followed by a
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single character. Octal and hexadecimal escape sequences are not
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supported.
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<p>Additionally, <code>printf</code> supports conversion specifications for DFP
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(<dfn>Decimal Floating Point</dfn>) types using the following length modifiers
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together with a floating point specifier.
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letters:
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<ul>
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<li>‘<samp><span class="samp">H</span></samp>’ for printing <code>Decimal32</code> types.
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<li>‘<samp><span class="samp">D</span></samp>’ for printing <code>Decimal64</code> types.
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<li>‘<samp><span class="samp">DD</span></samp>’ for printing <code>Decimal128</code> types.
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</ul>
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<p>If the underlying <code>C</code> implementation used to build <span class="sc">gdb</span> has
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support for the three length modifiers for DFP types, other modifiers
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such as width and precision will also be available for <span class="sc">gdb</span> to use.
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<p>In case there is no such <code>C</code> support, no additional modifiers will be
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available and the value will be printed in the standard way.
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<p>Here's an example of printing DFP types using the above conversion letters:
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<pre class="smallexample"> printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
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</pre>
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<p><a name="eval"></a><a name="index-eval-1830"></a><br><dt><code>eval </code><var>template</var><code>, </code><var>expressions</var><code>...</code><dd>Convert the values of one or more <var>expressions</var> under the control of
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the string <var>template</var> to a command line, and call it.
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</dl>
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</body></html>
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