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<a name="The-unwind_005fprotect-Statement"></a>
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<p>
Next: <a href="The-try-Statement.html#The-try-Statement" accesskey="n" rel="next">The try Statement</a>, Previous: <a href="The-continue-Statement.html#The-continue-Statement" accesskey="p" rel="prev">The continue Statement</a>, Up: <a href="Statements.html#Statements" accesskey="u" rel="up">Statements</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="The-unwind_005fprotect-Statement-1"></a>
<h3 class="section">10.8 The unwind_protect Statement</h3>
<a name="index-unwind_005fprotect-statement"></a>
<a name="index-unwind_005fprotect_005fcleanup"></a>
<a name="index-end_005funwind_005fprotect"></a>
<p>Octave supports a limited form of exception handling modeled after the
unwind-protect form of Lisp.
</p>
<p>The general form of an <code>unwind_protect</code> block looks like this:
</p>
<div class="example">
<pre class="example">unwind_protect
<var>body</var>
unwind_protect_cleanup
<var>cleanup</var>
end_unwind_protect
</pre></div>
<p>where <var>body</var> and <var>cleanup</var> are both optional and may contain any
Octave expressions or commands. The statements in <var>cleanup</var> are
guaranteed to be executed regardless of how control exits <var>body</var>.
</p>
<p>This is useful to protect temporary changes to global variables from
possible errors. For example, the following code will always restore
the original value of the global variable <code>frobnosticate</code>
even if an error occurs in the first part of the <code>unwind_protect</code>
block.
</p>
<div class="example">
<pre class="example">save_frobnosticate = frobnosticate;
unwind_protect
frobnosticate = true;
…
unwind_protect_cleanup
frobnosticate = save_frobnosticate;
end_unwind_protect
</pre></div>
<p>Without <code>unwind_protect</code>, the value of <var>frobnosticate</var>
would not be restored if an error occurs while evaluating the first part
of the <code>unwind_protect</code> block because evaluation would stop at the
point of the error and the statement to restore the value would not be
executed.
</p>
<p>In addition to unwind_protect, Octave supports another form of
exception handling, the <code>try</code> block.
</p>
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