Unlike static member functions or free functions, non-static member functions won’t implicitly convert to member function pointers.
(emphasis mine)
An lvalue of function type
T
can be implicitly converted to a prvalue pointer to that function. This does not apply to non-static member functions because lvalues that refer to non-static member functions do not exist.
So you need to use &
explicitly to take the address of the non-static member functions (i.e. to get non-static member function pointers). e.g.
void(Machine:: *ptrs[])() = { &Machine::off, &Machine::on };
If you declare them as static member function, you should change the type of ptrs
(to array of non-member function pointers). Note that for static member function it’s fine to not use &
explicitly. e.g.
void(*ptrs[])() = { Machine::off, Machine::on };