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Previous: <a href="Catching-Errors.html" accesskey="p" rel="prev">Catching Errors</a>, Up: <a href="Handling-Errors.html" accesskey="u" rel="up">Handling Errors</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<h4 class="subsection" id="Recovering-From-Errors-1"><span>12.1.3 Recovering From Errors<a class="copiable-link" href="#Recovering-From-Errors-1"> ¶</a></span></h4>
<p>Octave provides several ways of recovering from errors. There are
<code class="code">try</code>/<code class="code">catch</code> blocks,
<code class="code">unwind_protect</code>/<code class="code">unwind_protect_cleanup</code> blocks,
and finally the <code class="code">onCleanup</code> command.
</p>
<p>The <code class="code">onCleanup</code> command associates an ordinary Octave variable (the
trigger) with an arbitrary function (the action). Whenever the Octave variable
ceases to exist—whether due to a function return, an error, or simply because
the variable has been removed with <code class="code">clear</code>—then the assigned function
is executed.
</p>
<p>The function can do anything necessary for cleanup such as closing open file
handles, printing an error message, or restoring global variables to their
initial values. The last example is a very convenient idiom for Octave code.
For example:
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">function rand42
old_state = rand ("state");
restore_state = onCleanup (@() rand ("state", old_state));
rand ("state", 42);
...
endfunction # rand generator state restored by onCleanup
</pre></div></div>
<a class="anchor" id="XREFonCleanup"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-onCleanup"><span><code class="def-type"><var class="var">obj</var> =</code> <strong class="def-name">onCleanup</strong> <code class="def-code-arguments">(<var class="var">function</var>)</code><a class="copiable-link" href="#index-onCleanup"> ¶</a></span></dt>
<dd><p>Create a special object that executes a given <var class="var">function</var> upon destruction.
</p>
<p>If the object is copied to multiple variables (or cell or struct array
elements) or returned from a function, then <var class="var">function</var> will be executed
only after the last copy of the object is cleared.
</p>
<p>The input <var class="var">function</var> is a handle to a function. The handle may point to an
anonymous function in order to directly place commands in the <code class="code">onCleanup</code>
call.
</p>
<p>Programming Note: If multiple local <code class="code">onCleanup</code> variables are created, the
order in which they are called is unspecified. For similar functionality
See <a class="xref" href="The-unwind_005fprotect-Statement.html">The unwind_protect Statement</a>.
</p>
<p>Example
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">octave:1> trigger = onCleanup (@() disp ('onCleanup was executed'));
octave:2> clear trigger
onCleanup was executed
octave:3
</pre></div></div>
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