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:
-fobjc-exceptions
command line option must be used when compiling Objective-C files that use exceptions. -fexceptions
and -shared-libgcc
options are used when linking. 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
).
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-4.9.3/gcc/Exceptions.html