C function name or function pointer? [duplicate]

Question

Let's see this code:

#include <stdio.h>

typedef int (*callback) (void *arg);
callback world = NULL;

int f(void *_) {
    printf("World!");
    return 0;
}

int main() {
    printf("Hello, ");
    // world = f;
    world = &f; // both works
    if (world != NULL) {
        world(NULL);
    }
}

When setting world variable, both world = f; and world = &f; works.

Which should I use? Does it depend on the compiler or C version?

% gcc -v
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 8.0.0 (clang-800.0.38)
Target: x86_64-apple-darwin15.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

Answer 1

Both world = f; and world = &f; works because there is no difference between f and &f when passing it as an argument.

See C99 specification (section 6.7.5.3.8).

A declaration of a parameter as ‘‘function returning type’’ shall be adjusted to ‘‘pointer to function returning type’’, as in 6.3.2.1.