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<title>Debugging with GDB: Breakpoints</title>

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<a name="Breakpoints"></a>
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<p>
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> &nbsp; [<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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<hr>
<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.
</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 &lsquo;<samp>a + b</samp>&rsquo;.  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-breakpoint-lists"></a>
<a name="index-ranges-of-breakpoints"></a>
<a name="index-lists-of-breakpoints"></a>
<p>Some <small>GDB</small> commands accept a space-separated list of breakpoints
on which to operate.  A list element can be either a single breakpoint number,
like &lsquo;<samp>5</samp>&rsquo;, or a range of such numbers, like &lsquo;<samp>5-7</samp>&rsquo;.
When a breakpoint list is given to a command, all breakpoints in that list
are operated on.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Set-Breaks.html#Set-Breaks" accesskey="1">Set Breaks</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Setting breakpoints
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Set-Watchpoints.html#Set-Watchpoints" accesskey="2">Set Watchpoints</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Setting watchpoints
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Set-Catchpoints.html#Set-Catchpoints" accesskey="3">Set Catchpoints</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Setting catchpoints
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Delete-Breaks.html#Delete-Breaks" accesskey="4">Delete Breaks</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Deleting breakpoints
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Disabling.html#Disabling" accesskey="5">Disabling</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Disabling breakpoints
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Conditions.html#Conditions" accesskey="6">Conditions</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Break conditions
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Break-Commands.html#Break-Commands" accesskey="7">Break Commands</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Breakpoint command lists
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Dynamic-Printf.html#Dynamic-Printf" accesskey="8">Dynamic Printf</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Dynamic printf
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Save-Breakpoints.html#Save-Breakpoints" accesskey="9">Save Breakpoints</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How to save breakpoints in a file
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Static-Probe-Points.html#Static-Probe-Points">Static Probe Points</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Listing static probe points
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Error-in-Breakpoints.html#Error-in-Breakpoints">Error in Breakpoints</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">&ldquo;Cannot insert breakpoints&rdquo;
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Breakpoint_002drelated-Warnings.html#Breakpoint_002drelated-Warnings">Breakpoint-related Warnings</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">&ldquo;Breakpoint address adjusted...&rdquo;
</td></tr>
</table>

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