<html lang="en">
<head>
<title>Exceptions - Using the GNU Compiler Collection (GCC)</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Using the GNU Compiler Collection (GCC)">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="Objective_002dC.html#Objective_002dC" title="Objective-C">
<link rel="prev" href="compatibility_005falias.html#compatibility_005falias" title="compatibility_alias">
<link rel="next" href="Synchronization.html#Synchronization" title="Synchronization">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1988-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``Funding Free Software'', the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below). A copy of the license is included in the section entitled
``GNU Free Documentation License''.
(a) The FSF's Front-Cover Text is:
A GNU Manual
(b) The FSF's Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU
software. Copies published by the Free Software Foundation raise
funds for GNU development.-->
<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="Exceptions"></a>
<p>
Next: <a rel="next" accesskey="n" href="Synchronization.html#Synchronization">Synchronization</a>,
Previous: <a rel="previous" accesskey="p" href="compatibility_005falias.html#compatibility_005falias">compatibility_alias</a>,
Up: <a rel="up" accesskey="u" href="Objective_002dC.html#Objective_002dC">Objective-C</a>
<hr>
</div>
<h3 class="section">8.7 Exceptions</h3>
<p>GNU Objective-C provides exception support built into the language, as
in the following example:
<pre class="smallexample"> @try {
...
@throw expr;
...
}
@catch (AnObjCClass *exc) {
...
@throw expr;
...
@throw;
...
}
@catch (AnotherClass *exc) {
...
}
@catch (id allOthers) {
...
}
@finally {
...
@throw expr;
...
}
</pre>
<p>The <code>@throw</code> statement may appear anywhere in an Objective-C or
Objective-C++ program; when used inside of a <code>@catch</code> block, the
<code>@throw</code> may appear without an argument (as shown above), in
which case the object caught by the <code>@catch</code> will be rethrown.
<p>Note that only (pointers to) Objective-C objects may be thrown and
caught using this scheme. When an object is thrown, it will be caught
by the nearest <code>@catch</code> clause capable of handling objects of
that type, analogously to how <code>catch</code> blocks work in C++ and
Java. A <code>@catch(id ...)</code> clause (as shown above) may also
be provided to catch any and all Objective-C exceptions not caught by
previous <code>@catch</code> clauses (if any).
<p>The <code>@finally</code> clause, if present, will be executed upon exit
from the immediately preceding <code>@try ... @catch</code> section.
This will happen regardless of whether any exceptions are thrown,
caught or rethrown inside the <code>@try ... @catch</code> section,
analogously to the behavior of the <code>finally</code> clause in Java.
<p>There are several caveats to using the new exception mechanism:
<ul>
<li>The <samp><span class="option">-fobjc-exceptions</span></samp> command line option must be used when
compiling Objective-C files that use exceptions.
<li>With the GNU runtime, exceptions are always implemented as “native”
exceptions and it is recommended that the <samp><span class="option">-fexceptions</span></samp> and
<samp><span class="option">-shared-libgcc</span></samp> options are used when linking.
<li>With the NeXT runtime, although currently designed to be binary
compatible with <code>NS_HANDLER</code>-style idioms provided by the
<code>NSException</code> class, the new exceptions can only be used on Mac
OS X 10.3 (Panther) and later systems, due to additional functionality
needed in the NeXT Objective-C runtime.
<li>As mentioned above, the new exceptions do not support handling
types other than Objective-C objects. Furthermore, when used from
Objective-C++, the Objective-C exception model does not interoperate with C++
exceptions at this time. This means you cannot <code>@throw</code> an exception
from Objective-C and <code>catch</code> it in C++, or vice versa
(i.e., <code>throw ... @catch</code>).
</ul>
<!-- ========================================================================= -->
</body></html>