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| <title>Debugging with GDB: Breakpoints</title> |
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| Next: <a href="Continuing-and-Stepping.html#Continuing-and-Stepping" accesskey="n" rel="next">Continuing and Stepping</a>, Up: <a href="Stopping.html#Stopping" accesskey="u" rel="up">Stopping</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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| <a name="Breakpoints_002c-Watchpoints_002c-and-Catchpoints"></a> |
| <h3 class="section">5.1 Breakpoints, Watchpoints, and Catchpoints</h3> |
| |
| <a name="index-breakpoints"></a> |
| <p>A <em>breakpoint</em> makes your program stop whenever a certain point in |
| the program is reached. For each breakpoint, you can add conditions to |
| control in finer detail whether your program stops. You can set |
| breakpoints with the <code>break</code> command and its variants (see <a href="Set-Breaks.html#Set-Breaks">Setting Breakpoints</a>), to specify the place where your program |
| should stop by line number, function name or exact address in the |
| program. |
| </p> |
| <p>On some systems, you can set breakpoints in shared libraries before |
| the executable is run. There is a minor limitation on HP-UX systems: |
| you must wait until the executable is run in order to set breakpoints |
| in shared library routines that are not called directly by the program |
| (for example, routines that are arguments in a <code>pthread_create</code> |
| call). |
| </p> |
| <a name="index-watchpoints"></a> |
| <a name="index-data-breakpoints"></a> |
| <a name="index-memory-tracing"></a> |
| <a name="index-breakpoint-on-memory-address"></a> |
| <a name="index-breakpoint-on-variable-modification"></a> |
| <p>A <em>watchpoint</em> is a special breakpoint that stops your program |
| when the value of an expression changes. The expression may be a value |
| of a variable, or it could involve values of one or more variables |
| combined by operators, such as ‘<samp>a + b</samp>’. This is sometimes called |
| <em>data breakpoints</em>. You must use a different command to set |
| watchpoints (see <a href="Set-Watchpoints.html#Set-Watchpoints">Setting Watchpoints</a>), but aside |
| from that, you can manage a watchpoint like any other breakpoint: you |
| enable, disable, and delete both breakpoints and watchpoints using the |
| same commands. |
| </p> |
| <p>You can arrange to have values from your program displayed automatically |
| whenever <small>GDB</small> stops at a breakpoint. See <a href="Auto-Display.html#Auto-Display">Automatic Display</a>. |
| </p> |
| <a name="index-catchpoints"></a> |
| <a name="index-breakpoint-on-events"></a> |
| <p>A <em>catchpoint</em> is another special breakpoint that stops your program |
| when a certain kind of event occurs, such as the throwing of a C<tt>++</tt> |
| exception or the loading of a library. As with watchpoints, you use a |
| different command to set a catchpoint (see <a href="Set-Catchpoints.html#Set-Catchpoints">Setting |
| Catchpoints</a>), but aside from that, you can manage a catchpoint like any |
| other breakpoint. (To stop when your program receives a signal, use the |
| <code>handle</code> command; see <a href="Signals.html#Signals">Signals</a>.) |
| </p> |
| <a name="index-breakpoint-numbers"></a> |
| <a name="index-numbers-for-breakpoints"></a> |
| <p><small>GDB</small> assigns a number to each breakpoint, watchpoint, or |
| catchpoint when you create it; these numbers are successive integers |
| starting with one. In many of the commands for controlling various |
| features of breakpoints you use the breakpoint number to say which |
| breakpoint you want to change. Each breakpoint may be <em>enabled</em> or |
| <em>disabled</em>; if disabled, it has no effect on your program until you |
| enable it again. |
| </p> |
| <a name="index-breakpoint-ranges"></a> |
| <a name="index-ranges-of-breakpoints"></a> |
| <p>Some <small>GDB</small> commands accept a range of breakpoints on which to |
| operate. A breakpoint range is either a single breakpoint number, like |
| ‘<samp>5</samp>’, or two such numbers, in increasing order, separated by a |
| hyphen, like ‘<samp>5-7</samp>’. When a breakpoint range is given to a command, |
| all breakpoints in that range are operated on. |
| </p> |
| <table class="menu" border="0" cellspacing="0"> |
| <tr><td align="left" valign="top">• <a href="Set-Breaks.html#Set-Breaks" accesskey="1">Set Breaks</a>:</td><td> </td><td align="left" valign="top">Setting breakpoints |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Set-Watchpoints.html#Set-Watchpoints" accesskey="2">Set Watchpoints</a>:</td><td> </td><td align="left" valign="top">Setting watchpoints |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Set-Catchpoints.html#Set-Catchpoints" accesskey="3">Set Catchpoints</a>:</td><td> </td><td align="left" valign="top">Setting catchpoints |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Delete-Breaks.html#Delete-Breaks" accesskey="4">Delete Breaks</a>:</td><td> </td><td align="left" valign="top">Deleting breakpoints |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Disabling.html#Disabling" accesskey="5">Disabling</a>:</td><td> </td><td align="left" valign="top">Disabling breakpoints |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Conditions.html#Conditions" accesskey="6">Conditions</a>:</td><td> </td><td align="left" valign="top">Break conditions |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Break-Commands.html#Break-Commands" accesskey="7">Break Commands</a>:</td><td> </td><td align="left" valign="top">Breakpoint command lists |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Dynamic-Printf.html#Dynamic-Printf" accesskey="8">Dynamic Printf</a>:</td><td> </td><td align="left" valign="top">Dynamic printf |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Save-Breakpoints.html#Save-Breakpoints" accesskey="9">Save Breakpoints</a>:</td><td> </td><td align="left" valign="top">How to save breakpoints in a file |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Static-Probe-Points.html#Static-Probe-Points">Static Probe Points</a>:</td><td> </td><td align="left" valign="top">Listing static probe points |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Error-in-Breakpoints.html#Error-in-Breakpoints">Error in Breakpoints</a>:</td><td> </td><td align="left" valign="top">“Cannot insert breakpoints” |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Breakpoint_002drelated-Warnings.html#Breakpoint_002drelated-Warnings">Breakpoint-related Warnings</a>:</td><td> </td><td align="left" valign="top">“Breakpoint address adjusted...” |
| </td></tr> |
| </table> |
| |
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