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| <title>Debugging with GDB: Selection</title> |
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| <a name="Selection"></a> |
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| <a name="Selecting-a-Frame"></a> |
| <h3 class="section">8.4 Selecting a Frame</h3> |
| |
| <p>Most commands for examining the stack and other data in your program work on |
| whichever stack frame is selected at the moment. Here are the commands for |
| selecting a stack frame; all of them finish by printing a brief description |
| of the stack frame just selected. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-frame_002c-selecting"></a> |
| <a name="index-f-_0028frame_0029"></a> |
| </dd> |
| <dt><code>frame <var>n</var></code></dt> |
| <dt><code>f <var>n</var></code></dt> |
| <dd><p>Select frame number <var>n</var>. Recall that frame zero is the innermost |
| (currently executing) frame, frame one is the frame that called the |
| innermost one, and so on. The highest-numbered frame is the one for |
| <code>main</code>. |
| </p> |
| </dd> |
| <dt><code>frame <var>stack-addr</var> [ <var>pc-addr</var> ]</code></dt> |
| <dt><code>f <var>stack-addr</var> [ <var>pc-addr</var> ]</code></dt> |
| <dd><p>Select the frame at address <var>stack-addr</var>. This is useful mainly if the |
| chaining of stack frames has been damaged by a bug, making it |
| impossible for <small>GDB</small> to assign numbers properly to all frames. In |
| addition, this can be useful when your program has multiple stacks and |
| switches between them. The optional <var>pc-addr</var> can also be given to |
| specify the value of PC for the stack frame. |
| </p> |
| <a name="index-up"></a> |
| </dd> |
| <dt><code>up <var>n</var></code></dt> |
| <dd><p>Move <var>n</var> frames up the stack; <var>n</var> defaults to 1. For positive |
| numbers <var>n</var>, this advances toward the outermost frame, to higher |
| frame numbers, to frames that have existed longer. |
| </p> |
| <a name="index-down"></a> |
| <a name="index-do-_0028down_0029"></a> |
| </dd> |
| <dt><code>down <var>n</var></code></dt> |
| <dd><p>Move <var>n</var> frames down the stack; <var>n</var> defaults to 1. For |
| positive numbers <var>n</var>, this advances toward the innermost frame, to |
| lower frame numbers, to frames that were created more recently. |
| You may abbreviate <code>down</code> as <code>do</code>. |
| </p></dd> |
| </dl> |
| |
| <p>All of these commands end by printing two lines of output describing the |
| frame. The first line shows the frame number, the function name, the |
| arguments, and the source file and line number of execution in that |
| frame. The second line shows the text of that source line. |
| </p> |
| <p>For example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) up |
| #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) |
| at env.c:10 |
| 10 read_input_file (argv[i]); |
| </pre></div> |
| |
| <p>After such a printout, the <code>list</code> command with no arguments |
| prints ten lines centered on the point of execution in the frame. |
| You can also edit the program at the point of execution with your favorite |
| editing program by typing <code>edit</code>. |
| See <a href="List.html#List">Printing Source Lines</a>, |
| for details. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-down_002dsilently"></a> |
| <a name="index-up_002dsilently"></a> |
| </dd> |
| <dt><code>up-silently <var>n</var></code></dt> |
| <dt><code>down-silently <var>n</var></code></dt> |
| <dd><p>These two commands are variants of <code>up</code> and <code>down</code>, |
| respectively; they differ in that they do their work silently, without |
| causing display of the new frame. They are intended primarily for use |
| in <small>GDB</small> command scripts, where the output might be unnecessary and |
| distracting. |
| </p></dd> |
| </dl> |
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