1<html lang="en"> 2<head> 3<title>Output - Debugging with GDB</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Debugging with GDB"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Sequences.html#Sequences" title="Sequences"> 9<link rel="prev" href="Command-Files.html#Command-Files" title="Command Files"> 10<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 11<!-- 12Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 131998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 14Free Software Foundation, Inc. 15 16Permission is granted to copy, distribute and/or modify this document 17under the terms of the GNU Free Documentation License, Version 1.3 or 18any later version published by the Free Software Foundation; with the 19Invariant Sections being ``Free Software'' and ``Free Software Needs 20Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,'' 21and with the Back-Cover Texts as in (a) below. 22 23(a) The FSF's Back-Cover Text is: ``You are free to copy and modify 24this GNU Manual. 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This section 54describes three commands useful for generating exactly the output you 55want. 56 57 58<a name="index-echo-1562"></a> 59<dl><dt><code>echo </code><var>text</var><dd><!-- I do not consider backslash-space a standard C escape sequence --> 60<!-- because it is not in ANSI. --> 61Print <var>text</var>. Nonprinting characters can be included in 62<var>text</var> using C escape sequences, such as ‘<samp><span class="samp">\n</span></samp>’ to print a 63newline. <strong>No newline is printed unless you specify one.</strong> 64In addition to the standard C escape sequences, a backslash followed 65by a space stands for a space. This is useful for displaying a 66string with spaces at the beginning or the end, since leading and 67trailing spaces are otherwise trimmed from all arguments. 68To print ‘<samp><span class="samp"> <!-- /@w -->and foo = <!-- /@w --></span></samp>’, use the command 69‘<samp><span class="samp">echo \ <!-- /@w -->and foo = \ <!-- /@w --></span></samp>’. 70 71 <p>A backslash at the end of <var>text</var> can be used, as in C, to continue 72the command onto subsequent lines. For example, 73 74 <pre class="smallexample"> echo This is some text\n\ 75 which is continued\n\ 76 onto several lines.\n 77</pre> 78 <p>produces the same output as 79 80 <pre class="smallexample"> echo This is some text\n 81 echo which is continued\n 82 echo onto several lines.\n 83</pre> 84 <p><a name="index-output-1563"></a><br><dt><code>output </code><var>expression</var><dd>Print the value of <var>expression</var> and nothing but that value: no 85newlines, no ‘<samp><span class="samp">$</span><var>nn</var><span class="samp"> = </span></samp>’. The value is not entered in the 86value history either. See <a href="Expressions.html#Expressions">Expressions</a>, for more information 87on expressions. 88 89 <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 90the same formats as for <code>print</code>. See <a href="Output-Formats.html#Output-Formats">Output Formats</a>, for more information. 91 92 <p><a name="index-printf-1564"></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 93the string <var>template</var>. To print several values, make 94<var>expressions</var> be a comma-separated list of individual expressions, 95which may be either numbers or pointers. Their values are printed as 96specified by <var>template</var>, exactly as a C program would do by 97executing the code below: 98 99 <pre class="smallexample"> printf (<var>template</var>, <var>expressions</var>...); 100</pre> 101 <p>As in <code>C</code> <code>printf</code>, ordinary characters in <var>template</var> 102are printed verbatim, while <dfn>conversion specification</dfn> introduced 103by the ‘<samp><span class="samp">%</span></samp>’ character cause subsequent <var>expressions</var> to be 104evaluated, their values converted and formatted according to type and 105style information encoded in the conversion specifications, and then 106printed. 107 108 <p>For example, you can print two values in hex like this: 109 110 <pre class="smallexample"> printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo 111</pre> 112 <p><code>printf</code> supports all the standard <code>C</code> conversion 113specifications, including the flags and modifiers between the ‘<samp><span class="samp">%</span></samp>’ 114character and the conversion letter, with the following exceptions: 115 116 <ul> 117<li>The argument-ordering modifiers, such as ‘<samp><span class="samp">2$</span></samp>’, are not supported. 118 119 <li>The modifier ‘<samp><span class="samp">*</span></samp>’ is not supported for specifying precision or 120width. 121 122 <li>The ‘<samp><span class="samp">'</span></samp>’ flag (for separation of digits into groups according to 123<code>LC_NUMERIC'</code>) is not supported. 124 125 <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 126supported. 127 128 <li>The conversion letter ‘<samp><span class="samp">n</span></samp>’ (as in ‘<samp><span class="samp">%n</span></samp>’) is not supported. 129 130 <li>The conversion letters ‘<samp><span class="samp">a</span></samp>’ and ‘<samp><span class="samp">A</span></samp>’ are not supported. 131</ul> 132 133 <p class="noindent">Note that the ‘<samp><span class="samp">ll</span></samp>’ type modifier is supported only if the 134underlying <code>C</code> implementation used to build <span class="sc">gdb</span> supports 135the <code>long long int</code> type, and the ‘<samp><span class="samp">L</span></samp>’ type modifier is 136supported only if <code>long double</code> type is available. 137 138 <p>As in <code>C</code>, <code>printf</code> supports simple backslash-escape 139sequences, such as <code>\n</code>, ‘<samp><span class="samp">\t</span></samp>’, ‘<samp><span class="samp">\\</span></samp>’, ‘<samp><span class="samp">\"</span></samp>’, 140‘<samp><span class="samp">\a</span></samp>’, and ‘<samp><span class="samp">\f</span></samp>’, that consist of backslash followed by a 141single character. Octal and hexadecimal escape sequences are not 142supported. 143 144 <p>Additionally, <code>printf</code> supports conversion specifications for DFP 145(<dfn>Decimal Floating Point</dfn>) types using the following length modifiers 146together with a floating point specifier. 147letters: 148 149 <ul> 150<li>‘<samp><span class="samp">H</span></samp>’ for printing <code>Decimal32</code> types. 151 152 <li>‘<samp><span class="samp">D</span></samp>’ for printing <code>Decimal64</code> types. 153 154 <li>‘<samp><span class="samp">DD</span></samp>’ for printing <code>Decimal128</code> types. 155</ul> 156 157 <p>If the underlying <code>C</code> implementation used to build <span class="sc">gdb</span> has 158support for the three length modifiers for DFP types, other modifiers 159such as width and precision will also be available for <span class="sc">gdb</span> to use. 160 161 <p>In case there is no such <code>C</code> support, no additional modifiers will be 162available and the value will be printed in the standard way. 163 164 <p>Here's an example of printing DFP types using the above conversion letters: 165 <pre class="smallexample"> printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl 166</pre> 167 <p><a name="index-eval-1565"></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 168the string <var>template</var> to a command line, and call it. 169 170 </dl> 171 172 </body></html> 173 174