Question

I apologize if this was asked many times.
I’m trying to understand why both of this works fine without any warnings or other visible issues (in Xcode):

int testFunctionAcceptingIntPointer(int * p) {         
    return *p = *p +5;
}

void test() {
    int testY = 7;
    typedef int (*MyPointerToFunction)(int*);
    // Both this (simply a function name):
    MyPointerToFunction functionPointer = testFunctionAcceptingIntPointer;
    // And this works (pointer to function):
    MyPointerToFunction functionPointer = &testFunctionAcceptingIntPointer;
    int y = functionPointer(&testY);
}

Answer 1

The code works fine without warnings both ways because a function designator is converted to a function pointer

MyPointerToFunction functionPointer = testFunctionAcceptingIntPointer;

unless it is the operand of the address operator

MyPointerToFunction functionPointer = &testFunctionAcceptingIntPointer;

(or sizeof and _Alignof).

In the first assignment, you don’t use &, so the automatic conversion is done, resulting in a function pointer of appropriate type, in the second, you explicitly take the address, resulting in a function pointer of the appropriate type.