html/gdb/Output-Formats.html

<html lang="en">
<head>
<title>Output Formats - Debugging with GDB</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Debugging with GDB">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="Data.html#Data" title="Data">
<link rel="prev" href="Arrays.html#Arrays" title="Arrays">
<link rel="next" href="Memory.html#Memory" title="Memory">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``Free Software'' and ``Free Software Needs
Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below.

(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom.''-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
  pre.display { font-family:inherit }
  pre.format  { font-family:inherit }
  pre.smalldisplay { font-family:inherit; font-size:smaller }
  pre.smallformat  { font-family:inherit; font-size:smaller }
  pre.smallexample { font-size:smaller }
  pre.smalllisp    { font-size:smaller }
  span.sc    { font-variant:small-caps }
  span.roman { font-family:serif; font-weight:normal; }
  span.sansserif { font-family:sans-serif; font-weight:normal; }
--></style>
<link rel="stylesheet" type="text/css" href="../cs.css">
</head>
<body>
<div class="node">
<a name="Output-Formats"></a>
<p>
Next:&nbsp;<a rel="next" accesskey="n" href="Memory.html#Memory">Memory</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="Arrays.html#Arrays">Arrays</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="Data.html#Data">Data</a>
<hr>
</div>

<h3 class="section">10.5 Output Formats</h3>

<p><a name="index-formatted-output-517"></a><a name="index-output-formats-518"></a>By default, <span class="sc">gdb</span> prints a value according to its data type.  Sometimes
this is not what you want.  For example, you might want to print a number
in hex, or a pointer in decimal.  Or you might want to view data in memory
at a certain address as a character string or as an instruction.  To do
these things, specify an <dfn>output format</dfn> when you print a value.

   <p>The simplest use of output formats is to say how to print a value
already computed.  This is done by starting the arguments of the
<code>print</code> command with a slash and a format letter.  The format
letters supported are:

     <dl>
<dt><code>x</code><dd>Regard the bits of the value as an integer, and print the integer in
hexadecimal.

     <br><dt><code>d</code><dd>Print as integer in signed decimal.

     <br><dt><code>u</code><dd>Print as integer in unsigned decimal.

     <br><dt><code>o</code><dd>Print as integer in octal.

     <br><dt><code>t</code><dd>Print as integer in binary.  The letter &lsquo;<samp><span class="samp">t</span></samp>&rsquo; stands for &ldquo;two&rdquo;.
<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>

     <br><dt><code>a</code><dd><a name="index-unknown-address_002c-locating-519"></a><a name="index-locate-address-520"></a>Print as an address, both absolute in hexadecimal and as an offset from
the nearest preceding symbol.  You can use this format used to discover
where (in what function) an unknown address is located:

     <pre class="smallexample">          (gdb) p/a 0x54320
          $3 = 0x54320 &lt;_initialize_vx+396&gt;
</pre>
     <p class="noindent">The command <code>info symbol 0x54320</code> yields similar results.
See <a href="Symbols.html#Symbols">info symbol</a>.

     <br><dt><code>c</code><dd>Regard as an integer and print it as a character constant.  This
prints both the numerical value and its character representation.  The
character representation is replaced with the octal escape &lsquo;<samp><span class="samp">\nnn</span></samp>&rsquo;
for characters outside the 7-bit <span class="sc">ascii</span> range.

     <p>Without this format, <span class="sc">gdb</span> displays <code>char</code>,
<code>unsigned&nbsp;char</code><!-- /@w -->, and <code>signed&nbsp;char</code><!-- /@w --> data as character
constants.  Single-byte members of vectors are displayed as integer
data.

     <br><dt><code>f</code><dd>Regard the bits of the value as a floating point number and print
using typical floating point syntax.

     <br><dt><code>s</code><dd><a name="index-printing-strings-521"></a><a name="index-printing-byte-arrays-522"></a>Regard as a string, if possible.  With this format, pointers to single-byte
data are displayed as null-terminated strings and arrays of single-byte data
are displayed as fixed-length strings.  Other values are displayed in their
natural types.

     <p>Without this format, <span class="sc">gdb</span> displays pointers to and arrays of
<code>char</code>, <code>unsigned&nbsp;char</code><!-- /@w -->, and <code>signed&nbsp;char</code><!-- /@w --> as
strings.  Single-byte members of a vector are displayed as an integer
array.

     <br><dt><code>r</code><dd><a name="index-raw-printing-523"></a>Print using the &lsquo;<samp><span class="samp">raw</span></samp>&rsquo; formatting.  By default, <span class="sc">gdb</span> will
use a Python-based pretty-printer, if one is available (see <a href="Pretty-Printing.html#Pretty-Printing">Pretty Printing</a>).  This typically results in a higher-level display of the
value's contents.  The &lsquo;<samp><span class="samp">r</span></samp>&rsquo; format bypasses any Python
pretty-printer which might exist.
</dl>

   <p>For example, to print the program counter in hex (see <a href="Registers.html#Registers">Registers</a>), type

<pre class="smallexample">     p/x $pc
</pre>
   <p class="noindent">Note that no space is required before the slash; this is because command
names in <span class="sc">gdb</span> cannot contain a slash.

   <p>To reprint the last value in the value history with a different format,
you can use the <code>print</code> command with just a format and no
expression.  For example, &lsquo;<samp><span class="samp">p/x</span></samp>&rsquo; reprints the last value in hex.

   <div class="footnote">
<hr>
<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> &lsquo;<samp><span class="samp">b</span></samp>&rsquo; cannot be used because these format letters are also
used with the <code>x</code> command, where &lsquo;<samp><span class="samp">b</span></samp>&rsquo; stands for &ldquo;byte&rdquo;;
see <a href="Memory.html#Memory">Examining Memory</a>.</p>

   <hr></div>

   </body></html>