Using "void" in C

Question

I'm confused about why we need to pass void into C functions:

int f(void) { return 0; }

versus

int f() { return 0; }

What is the proper thing to do and why?

Answer 1

In C, int f() is an old-style declaration. It says that f expects a fixed but unspecified number and type(s) of arguments. For example, given int f() { return 0; }, the compiler won't complain about f(42), or f("hello, world") (though the behavior of such a call is undefined).

int f(void) explicitly says that f takes no arguments.

(C++ has different rules; Stroustrup wasn't as concerned about backward compatibility with old C code.)

Answer 2

It's a vestige of C.

f(void) takes no arguments, so f(1) is invalid.

f() means that the parameters are unspecified, so f(1) is valid here.