### 10.8 The unwind_protect Statement ¶

Octave supports a limited form of exception handling modeled after the unwind-protect form of Lisp.

The general form of an `unwind_protect` block looks like this:

    unwind_protect
      body
    unwind_protect_cleanup
      cleanup
    end_unwind_protect

where body and cleanup are both optional and may contain any Octave expressions or commands. The statements in cleanup are guaranteed to be executed regardless of how control exits body.

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 `frobnosticate` even if an error occurs in the first part of the `unwind_protect` block.

    save_frobnosticate = frobnosticate;
    unwind_protect
      frobnosticate = true;
      ...
    unwind_protect_cleanup
      frobnosticate = save_frobnosticate;
    end_unwind_protect

Without `unwind_protect`, the value of frobnosticate would not be restored if an error occurs while evaluating the first part of the `unwind_protect` block because evaluation would stop at the point of the error and the statement to restore the value would not be executed.

In addition to unwind_protect, Octave supports another form of exception handling, the `try` block.