| <html lang="en"> |
| <head> |
| <title>Auto Display - 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="Memory.html#Memory" title="Memory"> |
| <link rel="next" href="Print-Settings.html#Print-Settings" title="Print Settings"> |
| <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="Auto-Display"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Print-Settings.html#Print-Settings">Print Settings</a>, |
| Previous: <a rel="previous" accesskey="p" href="Memory.html#Memory">Memory</a>, |
| Up: <a rel="up" accesskey="u" href="Data.html#Data">Data</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">10.7 Automatic Display</h3> |
| |
| <p><a name="index-automatic-display-530"></a><a name="index-display-of-expressions-531"></a> |
| If you find that you want to print the value of an expression frequently |
| (to see how it changes), you might want to add it to the <dfn>automatic |
| display list</dfn> so that <span class="sc">gdb</span> prints its value each time your program stops. |
| Each expression added to the list is given a number to identify it; |
| to remove an expression from the list, you specify that number. |
| The automatic display looks like this: |
| |
| <pre class="smallexample"> 2: foo = 38 |
| 3: bar[5] = (struct hack *) 0x3804 |
| </pre> |
| <p class="noindent">This display shows item numbers, expressions and their current values. As with |
| displays you request manually using <code>x</code> or <code>print</code>, you can |
| specify the output format you prefer; in fact, <code>display</code> decides |
| whether to use <code>print</code> or <code>x</code> depending your format |
| specification—it uses <code>x</code> if you specify either the ‘<samp><span class="samp">i</span></samp>’ |
| or ‘<samp><span class="samp">s</span></samp>’ format, or a unit size; otherwise it uses <code>print</code>. |
| |
| |
| <a name="index-display-532"></a> |
| <dl><dt><code>display </code><var>expr</var><dd>Add the expression <var>expr</var> to the list of expressions to display |
| each time your program stops. See <a href="Expressions.html#Expressions">Expressions</a>. |
| |
| <p><code>display</code> does not repeat if you press <RET> again after using it. |
| |
| <br><dt><code>display/</code><var>fmt</var> <var>expr</var><dd>For <var>fmt</var> specifying only a display format and not a size or |
| count, add the expression <var>expr</var> to the auto-display list but |
| arrange to display it each time in the specified format <var>fmt</var>. |
| See <a href="Output-Formats.html#Output-Formats">Output Formats</a>. |
| |
| <br><dt><code>display/</code><var>fmt</var> <var>addr</var><dd>For <var>fmt</var> ‘<samp><span class="samp">i</span></samp>’ or ‘<samp><span class="samp">s</span></samp>’, or including a unit-size or a |
| number of units, add the expression <var>addr</var> as a memory address to |
| be examined each time your program stops. Examining means in effect |
| doing ‘<samp><span class="samp">x/</span><var>fmt</var> <var>addr</var></samp>’. See <a href="Memory.html#Memory">Examining Memory</a>. |
| </dl> |
| |
| <p>For example, ‘<samp><span class="samp">display/i $pc</span></samp>’ can be helpful, to see the machine |
| instruction about to be executed each time execution stops (‘<samp><span class="samp">$pc</span></samp>’ |
| is a common name for the program counter; see <a href="Registers.html#Registers">Registers</a>). |
| |
| |
| <a name="index-delete-display-533"></a> |
| <a name="index-undisplay-534"></a> |
| <dl><dt><code>undisplay </code><var>dnums</var><code>...</code><dt><code>delete display </code><var>dnums</var><code>...</code><dd>Remove item numbers <var>dnums</var> from the list of expressions to display. |
| |
| <p><code>undisplay</code> does not repeat if you press <RET> after using it. |
| (Otherwise you would just get the error ‘<samp><span class="samp">No display number ...</span></samp>’.) |
| |
| <p><a name="index-disable-display-535"></a><br><dt><code>disable display </code><var>dnums</var><code>...</code><dd>Disable the display of item numbers <var>dnums</var>. A disabled display |
| item is not printed automatically, but is not forgotten. It may be |
| enabled again later. |
| |
| <p><a name="index-enable-display-536"></a><br><dt><code>enable display </code><var>dnums</var><code>...</code><dd>Enable display of item numbers <var>dnums</var>. It becomes effective once |
| again in auto display of its expression, until you specify otherwise. |
| |
| <br><dt><code>display</code><dd>Display the current values of the expressions on the list, just as is |
| done when your program stops. |
| |
| <p><a name="index-info-display-537"></a><br><dt><code>info display</code><dd>Print the list of expressions previously set up to display |
| automatically, each one with its item number, but without showing the |
| values. This includes disabled expressions, which are marked as such. |
| It also includes expressions which would not be displayed right now |
| because they refer to automatic variables not currently available. |
| </dl> |
| |
| <p><a name="index-display-disabled-out-of-scope-538"></a>If a display expression refers to local variables, then it does not make |
| sense outside the lexical context for which it was set up. Such an |
| expression is disabled when execution enters a context where one of its |
| variables is not defined. For example, if you give the command |
| <code>display last_char</code> while inside a function with an argument |
| <code>last_char</code>, <span class="sc">gdb</span> displays this argument while your program |
| continues to stop inside that function. When it stops elsewhere—where |
| there is no variable <code>last_char</code>—the display is disabled |
| automatically. The next time your program stops where <code>last_char</code> |
| is meaningful, you can enable the display expression once again. |
| |
| </body></html> |
| |
