Next: Synchronization, Previous: compatibility_alias, Up: Objective-C [Contents][Index]
GNU Objective-C provides exception support built into the language, as in the following example:
@try { @throw expr; } @catch (AnObjCClass *exc) { @throw expr; @throw; } @catch (AnotherClass *exc) { } @catch (id allOthers) { } @finally { @throw expr; }
The @throw
statement may appear anywhere in an Objective-C or Objective-C++ program; when used inside of a @catch
block, the @throw
may appear without an argument (as shown above), in which case the object caught by the @catch
will be rethrown.
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 @catch
clause capable of handling objects of that type, analogously to how catch
blocks work in C++ and Java. A @catch(id )
clause (as shown above) may also be provided to catch any and all Objective-C exceptions not caught by previous @catch
clauses (if any).
The @finally
clause, if present, will be executed upon exit from the immediately preceding @try @catch
section. This will happen regardless of whether any exceptions are thrown, caught or rethrown inside the @try @catch
section, analogously to the behavior of the finally
clause in Java.
There are several caveats to using the new exception mechanism:
NS_HANDLER
-style idioms provided by the NSException
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.@throw
an exception from Objective-C and catch
it in C++, or vice versa (i.e., throw @catch
).Next: Synchronization, Previous: compatibility_alias, Up: Objective-C [Contents][Index]