A simple exception handling framework for C language, using non-local jump functions setjmp and longjmp.
The pseudo keywords (try, catch and finally) are macros based on setjmp and longjmp. Whenever we start a try ... catch ... finally block, a non-local jump buffer is pushed at the top of a jump stack and is popped before exception handling in catch clause. So that, we can rethrow a caught exception. Otherwise, if the current jump buffer is not popped, any longjmp will cause infinite loop.
We can catch exceptions (usually unsigned integers) with try ... catch ... finally blocks.
try {
// code that may throw exceptions
} catch(exception1) {
// code that processes the exception1
} catch(exception2) {
// code that processes the exception2
} finally {
// defautl exception handling
// code that processes other exceptions
}
Note: we can fetch the exception code (an integer) by accessing variable _except_code_ inside try ... catch ... finally blocks.
We can throw an integer (non-zero) as an exception, for example:
throw(1);
This framework provides basic exception handling with setjmp and longjmp, and is not a full-blown exception machansim like C++. So, there are a few ceveats and limitations:
- After invoking longjmp(), non-volatile-qualified local objects should not be accessed if their values could have changed since the invocation of setjmp(). Their value in this case is considered indeterminate, and accessing them is undefined behavior.
- Don't
returndirectly in thetry ... catch ... finallyblocks. - Memory allocated within
try ... catch ... finallyblocks is not automatically released when an exception is thrown. - The semantics of
finallyclause is different from that in Java. - A caught exception can be rethrown.
- The
try ... catch ... finallyblocks can be nested. It's recommended to use{}beside statements. Otherwise, using_except_code_will fail.