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<title>Debugging with GDB: Output</title>
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<a name="Output"></a>
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<div class="header">
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<p>
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Next: <a href="Auto_002dloading-sequences.html#Auto_002dloading-sequences" accesskey="n" rel="next">Auto-loading sequences</a>, Previous: <a href="Command-Files.html#Command-Files" accesskey="p" rel="previous">Command Files</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</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="Commands-for-Controlled-Output"></a>
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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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<small>GDB</small> 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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</p>
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<dl compact="compact">
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<dd><a name="index-echo"></a>
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</dd>
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<dt><code>echo <var>text</var></code></dt>
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<dd><p>Print <var>text</var>. Nonprinting characters can be included in
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<var>text</var> using C escape sequences, such as ‘<samp>\n</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> <!-- /@w -->and foo = <!-- /@w --></samp>’, use the command
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‘<samp>echo \ <!-- /@w -->and foo = \ <!-- /@w --></samp>’.
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</p>
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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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</p>
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<div class="smallexample">
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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></div>
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<p>produces the same output as
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</p>
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<div class="smallexample">
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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></div>
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<a name="index-output"></a>
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</dd>
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<dt><code>output <var>expression</var></code></dt>
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<dd><p>Print the value of <var>expression</var> and nothing but that value: no
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newlines, no ‘<samp>$<var>nn</var> = </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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</p>
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</dd>
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<dt><code>output/<var>fmt</var> <var>expression</var></code></dt>
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<dd><p>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
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Formats</a>, for more information.
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</p>
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<a name="index-printf"></a>
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</dd>
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<dt><code>printf <var>template</var>, <var>expressions</var>…</code></dt>
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<dd><p>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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</p>
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<div class="smallexample">
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<pre class="smallexample">printf (<var>template</var>, <var>expressions</var>…);
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</pre></div>
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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 <em>conversion specification</em> introduced
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by the ‘<samp>%</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>
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<p>For example, you can print two values in hex like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
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</pre></div>
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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>%</samp>’
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character and the conversion letter, with the following exceptions:
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</p>
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<ul>
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<li> The argument-ordering modifiers, such as ‘<samp>2$</samp>’, are not supported.
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</li><li> The modifier ‘<samp>*</samp>’ is not supported for specifying precision or
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width.
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</li><li> The ‘<samp>'</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><li> The type modifiers ‘<samp>hh</samp>’, ‘<samp>j</samp>’, ‘<samp>t</samp>’, and ‘<samp>z</samp>’ are not
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supported.
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</li><li> The conversion letter ‘<samp>n</samp>’ (as in ‘<samp>%n</samp>’) is not supported.
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</li><li> The conversion letters ‘<samp>a</samp>’ and ‘<samp>A</samp>’ are not supported.
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</li></ul>
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<p>Note that the ‘<samp>ll</samp>’ type modifier is supported only if the
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underlying <code>C</code> implementation used to build <small>GDB</small> supports
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the <code>long long int</code> type, and the ‘<samp>L</samp>’ type modifier is
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supported only if <code>long double</code> type is available.
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</p>
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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>\t</samp>’, ‘<samp>\\</samp>’, ‘<samp>\"</samp>’,
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‘<samp>\a</samp>’, and ‘<samp>\f</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>
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<p>Additionally, <code>printf</code> supports conversion specifications for DFP
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(<em>Decimal Floating Point</em>) 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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</p>
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<ul>
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<li> ‘<samp>H</samp>’ for printing <code>Decimal32</code> types.
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</li><li> ‘<samp>D</samp>’ for printing <code>Decimal64</code> types.
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</li><li> ‘<samp>DD</samp>’ for printing <code>Decimal128</code> types.
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</li></ul>
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<p>If the underlying <code>C</code> implementation used to build <small>GDB</small> 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 <small>GDB</small> to use.
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</p>
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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>
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<p>Here’s an example of printing DFP types using the above conversion letters:
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</p><div class="smallexample">
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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></div>
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<a name="eval"></a><a name="index-eval"></a>
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</dd>
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<dt><code>eval <var>template</var>, <var>expressions</var>…</code></dt>
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<dd><p>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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</p>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Auto_002dloading-sequences.html#Auto_002dloading-sequences" accesskey="n" rel="next">Auto-loading sequences</a>, Previous: <a href="Command-Files.html#Command-Files" accesskey="p" rel="previous">Command Files</a>, Up: <a href="Sequences.html#Sequences" accesskey="u" rel="up">Sequences</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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