Yes there is: void foo(void* p=0); // has exactly the same ABI as void bar(void* p); bar(); // error: missing parameter foo(); // shorthand for foo(0);

Yes there is: void foo(void* p=0); // has exactly the same ABI as void bar(void* p); bar(); // error: missing parameter foo(); // shorthand for foo(0); // void(*)(void*) is a different type than void(*)(void*=0) // but they can be implicitly converted the same as // eg void* and char*