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<h3 class="section">13.3 Breakpoints</h3>
<p>Breakpoints can be set in any Octave function, using the <code>dbstop</code>
function.
<!-- debug.cc -->
<p><a name="doc_002ddbstop"></a>
<div class="defun">
— Loadable Function: <var>rline</var> = <b>dbstop</b> (<var>func, line, <small class="dots">...</small></var>)<var><a name="index-dbstop-693"></a></var><br>
<blockquote><p>Set a breakpoint in a function
<dl>
<dt><code>func</code><dd>String representing the function name. When already in debug
mode this should be left out and only the line should be given.
<br><dt><code>line</code><dd>Line number you would like the breakpoint to be set on. Multiple
lines might be given as separate arguments or as a vector.
</dl>
<p>The rline returned is the real line that the breakpoint was set at.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002ddbclear.html#doc_002ddbclear">dbclear</a>, <a href="doc_002ddbstatus.html#doc_002ddbstatus">dbstatus</a>, <a href="doc_002ddbstep.html#doc_002ddbstep">dbstep</a>.
</p></blockquote></div>
<p class="noindent">Note that breakpoints cannot be set in built-in functions
(e.g., <code>sin</code>, etc.) or dynamically loaded function (i.e., oct-files). To
set a breakpoint immediately on entering a function, the breakpoint
should be set to line 1. The leading comment block will be ignored and
the breakpoint will be set to the first executable statement in the
function. For example
<pre class="example"> dbstop ("asind", 1)
⇒ 27
</pre>
<p class="noindent">Note that the return value of <code>27</code> means that the breakpoint was
effectively set to line 27. The status of breakpoints in a function can
be queried with the <code>dbstatus</code> function.
<!-- debug.cc -->
<p><a name="doc_002ddbstatus"></a>
<div class="defun">
— Loadable Function: lst = <b>dbstatus</b> (<var>func</var>)<var><a name="index-dbstatus-694"></a></var><br>
<blockquote><p>Return a vector containing the lines on which a function has
breakpoints set.
<dl>
<dt><code>func</code><dd>String representing the function name. When already in debug
mode this should be left out.
</dl>
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<p class="noindent"><strong>See also:</strong> <a href="doc_002ddbclear.html#doc_002ddbclear">dbclear</a>, <a href="doc_002ddbwhere.html#doc_002ddbwhere">dbwhere</a>.
</p></blockquote></div>
<p class="noindent">Taking the above as an example, <code>dbstatus ("asind")</code> should return
27. The breakpoints can then be cleared with the <code>dbclear</code> function
<!-- debug.cc -->
<p><a name="doc_002ddbclear"></a>
<div class="defun">
— Loadable Function: <b>dbclear</b> (<var>func, line, <small class="dots">...</small></var>)<var><a name="index-dbclear-695"></a></var><br>
<blockquote><p>Delete a breakpoint in a function
<dl>
<dt><code>func</code><dd>String representing the function name. When already in debug
mode this should be left out and only the line should be given.
<br><dt><code>line</code><dd>Line number where you would like to remove the breakpoint. Multiple
lines might be given as separate arguments or as a vector.
</dl>
No checking is done to make sure that the line you requested is really
a breakpoint. If you get the wrong line nothing will happen.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002ddbstop.html#doc_002ddbstop">dbstop</a>, <a href="doc_002ddbstatus.html#doc_002ddbstatus">dbstatus</a>, <a href="doc_002ddbwhere.html#doc_002ddbwhere">dbwhere</a>.
</p></blockquote></div>
<p class="noindent">These functions can be used to clear all the breakpoints in a function. For example,
<pre class="example"> dbclear ("asind", dbstatus ("asind"));
</pre>
<p>A breakpoint can be set in a subfunction. For example if a file contains
the functions
<pre class="example"> function y = func1 (x)
y = func2 (x);
endfunction
function y = func2 (x)
y = x + 1;
endfunction
</pre>
<p class="noindent">then a breakpoint can be set at the start of the subfunction directly
with
<pre class="example"> dbstop (["func1", filemarker(), "func2"])
⇒ 5
</pre>
<p>Note that <code>filemarker</code> returns a character that marks the
subfunctions from the file containing them.
<p>Another simple way of setting a breakpoint in an Octave script is the
use of the <code>keyboard</code> function.
<!-- input.cc -->
<p><a name="doc_002dkeyboard"></a>
<div class="defun">
— Built-in Function: <b>keyboard</b> ()<var><a name="index-keyboard-696"></a></var><br>
— Built-in Function: <b>keyboard</b> (<var>prompt</var>)<var><a name="index-keyboard-697"></a></var><br>
<blockquote><p>This function is normally used for simple debugging. When the
<code>keyboard</code> function is executed, Octave prints a prompt and waits
for user input. The input strings are then evaluated and the results
are printed. This makes it possible to examine the values of variables
within a function, and to assign new values if necessary. To leave the
prompt and return to normal execution type ‘<samp><span class="samp">return</span></samp>’ or ‘<samp><span class="samp">dbcont</span></samp>’.
The <code>keyboard</code> function does not return an exit status.
<p>If <code>keyboard</code> is invoked without arguments, a default prompt of
‘<samp><span class="samp">debug> </span></samp>’ is used.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002ddbcont.html#doc_002ddbcont">dbcont</a>, <a href="doc_002ddbquit.html#doc_002ddbquit">dbquit</a>.
</p></blockquote></div>
<p class="noindent">The <code>keyboard</code> function is typically placed in a script at the
point where the user desires that the execution is stopped. It
automatically sets the running script into the debug mode.
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