Function pointer casting parameter to void

Question

I wrote a simple demo(test.cpp) for my question:

#include <stdio.h>
typedef void* (*SEL)(void);

int foo(int a, int b, int c) {
    return a + b + c;
}

SEL _ptr_to_foo() {
    return (SEL)foo;
}
int main() {
    SEL sel = _ptr_to_foo();

    return 0;
}

and I compiled it with g++ test.cpp -o test in my osx and compilers complained nothing.

But I'm confused about what happened here. As my opinion, SEL defines function pointer which parameter is void and returns void*. However, function foo should be a function which accepts three int parameters and returns an int as result. I think the function pointer of foo should be declared as something like int (*ptr)(int, int, int) = foo;. Why the casting in _ptr_to_foo works? What happened here?

Answer 1

c-style casts are fairly lax in their type checking. You should use static_cast instead. This fails to compile:

return static_cast<SEL>(foo);