What's the proper way to exit program in C?

Question

There are many ways how to exit program in C. Some of them are returning zero or error code, using exit function with EXIT_SUCCESS, EXIT_FAILURE, exit(0), exit(1) or some other error code, abort and probably few more I can't think of now.

My question is which option is the best and why. I'm asking here because every time I asked more experienced programmers this question, it ended up as a holy war.

Answer 1

I think the best thing is return EXIT_SUCCESS or return a non-zero number for which you have documented an error code, or EXIT_FAILURE if you can't define error codes for all the conditions that could cause you to fail. This would let a program using your program (in a pipe or batch function) actually use your error code to determine what to do next if applicable.

Personally I am not married to macros that always, on every single implementation on earth equal 0 but hey that sort of comment can get you downvoted.

Answer 2

There is no one "best". If you want to maximize portability, you can only use three values: EXIT_SUCCESS, EXIT_FALURE, and 0 (and 0 and EXIT_SUCCESS mean the same thing). If you don't mind losing some portability, it's often useful to return various other values to indicate why something failed, or (in some cases) return a non-zero value even in case of success to indicate things like how many of X it found, or carry the result of a calculation, etc.

As such, you have a choice between portability (but mostly to systems you probably don't care about, chiefly VMS) and functionality on a slightly reduced set of systems. You have to decide which is more important to you.

Edit: No, EXIT_SUCCESS does not always equal zero -- but (at least as far as the standard cares) the two mean the same thing. There was at least one compiler on VMS, however, that defined EXIT_SUCCESS to a non-zero value (VMS normally interpreted even numbers as failure and odd numbers as success, so EXIT_SUCCESS was defined to the proper odd number, and 0 was treated specially, so the system got an odd number when/if you returned it).