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