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