Problem - Kevin Tafuro

Exception handling essentially acts as an alternate return mechanism, designed particularly
for conditions that signify an abnormal state.
You can also perform exception handling in C using macros. The safe string-handling
library from Recipe 3.4 includes an exception-handling library named XXL.
This exception-handling library is also available separately at http://www.zork.org/
xxl/.
The XXLlibrary only allows you to throw integer exception codes. However, when
throwing an exception, you may also pass arbitrary data in a void pointer. The XXL
syntax attempts to look as much like C++ as possible, but is necessarily different
because of the limitations of C. Here is an example:
#include "xxl.h" /* Get definitions for exception handling. */
void sample(void) {
TRY {
somefunc( );
}
CATCH(1) {
/* Handle exception code 1. */
}
CATCH(2) {
/* Handle exception code 2. */
}
EXCEPT {
/* Handle all other exceptions... if you don't do this, they get propogated up
to previous callers. */
}
FINALLY {
/* This code always gets called after an exception handler, even if no
* exception gets thrown, or you raise a new exception. Additionally, if no
* handler catches the error, this code runs before the exception gets
* propogated.
*/
}
END_TRY;
There are a number of significant differences between XXLand C++ exception handling:
• In XXLyou can only catch a compile-time constant integer, whereas in C++ you
can catch based on a data type. That is, catch(2) is invalid in C++. There, you
would catch on the entire integer data type, as with catch(int x). You can think
of CATCH( ) in XXL as a sort of case statement in a big switch block.
• XXLhas the EXCEPT keyword, which catches any exception not explicitly caught
by a catch block. The EXCEPT block must follow all CATCH( ) blocks. XXL’s EXCEPT
keyword is equivalent to CATCH(...) in C++.
• XXLhas a FINALLY block, which, if used, must follow any exception-handling
blocks. The code in one of these blocks always runs, whether or not the excep-
702 | Chapter 13: Other Topics
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