What is a good general approach for deciding return values in C?

Question

My program is written in C for Linux, and has many functions with different patterns for return values:

1) one or two return n on success and -1

Answer 1

Not an actual answer to your question, but some random comments you might find interesting:

• it's normally obvious when to use case (1), but it gets ugly when unsigned types are involved - return (size_t)-1 still works, but it ain't pretty

• if you're using C99, there's nothing wrong with using _Bool; imo, it's a lot cleaner than just using an int

• I use return NULL instead of return 0 in pointer contexts (peronal preference), but I rarely check for it as I find it more natural to just treat the pointer as a boolean; a common case would look like this:

  struct foo *foo = create_foo();
  if(!foo) /* handle error */;
  

• I try to avoid case (2); using EXIT_SUCCESS and EXIT_FAILURE might be feasible, but imo this approach only makes sense if there are more than two possible outcomes and you'll have to use an enum anyway

• for more complicated programs, it might make sense to implement your own error handling scheme; there are some fairly advanced implementations using setjmp()/longjmp() around, but I prefer something errno-like with different variables for different types of errors