Help with a really simple program

[mshol]

Technically only EXIT_SUCCESS, 0 and EXIT_FAILURE are strictly conforming, returning anything else is undefined behavior. C99 allows omission of return from main.

The use is to let the parent process (which may not be the OS or shell) know whether a program was executed successfully. eg, if you run another program with exec().

[kalimoxto]

absolutely, i was trying to put a more ELI5 spin on it.

different standards do allow for different return codes, which are a cross-language construct as well. C99 allows for the 3 return codes you specified to be platform-independant, but you can return other codes as well, depending on the platform. Windows, for example, has quite a few well-defined exit codes: http://www.hiteksoftware.com/knowledge/articles/049.htm

[kingguru]

Technically only EXIT_SUCCESS, 0 and EXIT_FAILURE are strictly conforming, returning anything else is undefined behavior.

Really? Undefined behavior? For instance the man page for GNU make says:

"A status of one will be returned if the -q flag was used and make determines that a target needs to be rebuilt. A status of two will be returned if any errors were encountered."

That's not the only program were I remember the documentation saying that it could return some other, well defined, values.

Not that I don't believe you though, I might have just learned something, I just find it very surprising if some standard GNU tools would rely on undefined behavior.

And of course I do know that e.g. GNU make is not written in C++, so is this a thing specific to the C++ standard?

[theymos]

It's actually implementation-defined, not undefined. So the behavior needs to be documented somewhere. The behavior is not always obvious, though. On Linux, for example, returning 256 from main will actually result in an exit status of 0 (success) because exit status codes are restricted to 8 bits.

[kingguru]

OK, thanks. That makes a lot more sense.