Exception handling in C - making try catch work across functions

Question

I am writing an exception handling library in C and i ran into a bump:

#define TRY do{ jmp_buf ex_buf__; switch( setjmp(ex_buf__) ){ case 0:
#define FINALLY break; } default:
#define CATCH(x) break; case x:
#define ETRY } }while(0)
#define THROW(x) longjmp(ex_buf__, x)

In my current implementation of try catch throw, I won't be able to throw an exception from inside a method called from inside the try block because the jmp_buf variable is local. How would i make that possible? I thought about a global variable but that would not allow me to have nested try catch blocks.

Id on´t think this is possible without modifying *all* functions and function calls you have. C simply has no exceptions. — deviantfan, Feb 28 '14 at 13:07

score 4 · Accepted Answer · answered Feb 28 '14 at 13:11

4

You need to use a global jump buffer, because it needs to be visible to your "clients". You could, for example, save the old jump buffer in a try block, and restore it after its use.

In general, I would not recommend this approach at all, though. Trying to retrofit features into a language is fraught with peril, not the least of which would be the following code:

for ;; { 
  TRY {
    if (someVar) {
      break;
    }
  }
  FINALLY {
    doIt()
  }
  ETRY
}

answered Feb 28 '14 at 13:11

Norwæ

1,575
8
18

2

Agreed: it is not a good idea to try to implement Object-oriented specific features in `C`. If you "need" to do such a thing you probably had chosen the wrong language... – n0p Feb 28 '14 at 13:16
.. not that try/finally/catch has anything at all to do with object orientation. Which, incidentally, works just fine in C. – perh Feb 28 '14 at 13:33
Just a reminder that C++ is implemented in C.... Anyways this is a library for homework that I am making since it has to be done in C and i don't like C. Good approach though. Thanks a lot! – Jean-Luc Nacif Coelho Feb 28 '14 at 14:02
2

@Jean-LucNacifCoelho "C++ is implemented in C" - no. just no. – Andreas Grapentin Feb 28 '14 at 15:00

score 3 · Answer 2 · answered Dec 31 '14 at 17:38

3

Use a stack of jmp_buf's. Or better yet, use the existing CII library, which has been designed, built, and tested for this purpose.

answered Dec 31 '14 at 17:38

Norman Ramsey

198,648
61
360
533

1- Creating a local variable within a newly created scope suffices to save the context, as the compiler allows you to reuse variable names in different scopes. 2- "Use this already implemented library" is never a good answer. – Jean-Luc Nacif Coelho Jan 01 '15 at 21:05

Exception handling in C - making try catch work across functions

2 Answers2