c++ - Address operator with pointer to member function -

we know create "common" pointer function can example:

void fun(); void (*ptr)() = fun; 

the name of function address function start. not need use address operator & this:

void (*ptr)() = &fun; 

now pointer member function on contrary must use address operator. example class pointer member function ptr , function fun() must write:

void(a::*ptr)() = &a::fun; 

why difference?

it because function defined inside class. pointer member function holds "relative address" of function in class layout , have access way.

in case of static, has no pointer , behaves global function , so, can access normal function pointer.