<html lang="en"> <head> <title>The @code{unwind_protect} Statement - Untitled</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="Untitled"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="Statements.html#Statements" title="Statements"> <link rel="prev" href="The-_0040code_007bcontinue_007d-Statement.html#The-_0040code_007bcontinue_007d-Statement" title="The @code{continue} Statement"> <link rel="next" href="The-_0040code_007btry_007d-Statement.html#The-_0040code_007btry_007d-Statement" title="The @code{try} Statement"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="The-%3ccode%3eunwind_protect%3c%2fcode%3e-Statement"></a> <a name="The-_003ccode_003eunwind_005fprotect_003c_002fcode_003e-Statement"></a> <p> Next: <a rel="next" accesskey="n" href="The-_003ccode_003etry_003c_002fcode_003e-Statement.html#The-_003ccode_003etry_003c_002fcode_003e-Statement">The <code>try</code> Statement</a>, Previous: <a rel="previous" accesskey="p" href="The-_003ccode_003econtinue_003c_002fcode_003e-Statement.html#The-_003ccode_003econtinue_003c_002fcode_003e-Statement">The <code>continue</code> Statement</a>, Up: <a rel="up" accesskey="u" href="Statements.html#Statements">Statements</a> <hr> </div> <h3 class="section">10.8 The <code>unwind_protect</code> Statement</h3> <p><a name="index-g_t_0040code_007bunwind_005fprotect_007d-statement-575"></a><a name="index-g_t_0040code_007bunwind_005fprotect_005fcleanup_007d-576"></a><a name="index-g_t_0040code_007bend_005funwind_005fprotect_007d-577"></a> Octave supports a limited form of exception handling modelled after the unwind-protect form of Lisp. <p>The general form of an <code>unwind_protect</code> block looks like this: <pre class="example"> unwind_protect <var>body</var> unwind_protect_cleanup <var>cleanup</var> end_unwind_protect </pre> <p class="noindent">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>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. <pre class="example"> save_frobnosticate = frobnosticate; unwind_protect frobnosticate = true; ... unwind_protect_cleanup frobnosticate = save_frobnosticate; end_unwind_protect </pre> <p class="noindent">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. </body></html>