how to understand cls* (*) (int, double)

Question

I am working on some source codes grabbed from Internet and find a confused sentence.

map<int, Element* (*) (int, Domain*) > elemList

My question is for the value part of elemList. Is is a pointer ? Or constructor function? Or some else ?

Best regards

Answer 1

Element* (*) (int, Domain*) is for function pointers. These are of two types.

• Raw function pointers (which is something like this: void (*foo)(int x, int y);).
• Member function pointers (which looks something like this: void (Object::*foo)(int x, int y);).

In a raw function pointer, its made of 3 parts. Lets use the above example,

1. Return type (which is void).
2. Function name/ pointer name (which is foo).
3. Function parameters (which is (int x, int y)).

In a member function pointer, its made of 4 parts.

1. Return type (which is void).
2. Which class/ struct holds the function (which is Object).
3. Function name/ pointer name (which is foo).
4. Function parameters (which is (int x, int y)).

Calling a raw function pointer is as easy as this,

void Func(int x, int y) { ... }

void (*foo)(int x, int y) = Foo;    // Assigning the function pointer.
foo();    // Calling the pointer.

Calling a member function pointer is slightly different. For this you need a valid instance of the object.

class Object {
public:
    void Func(int x, int y) { ... }
};


void (Object::*foo)(int x, int y) = &Object::Func;    // Assigning the function pointer. Notice the '&' operator here.

Object object;
(object.*foo)();    // Calling the function pointer.

So what map<int, Element* (*) (int, Domain*) > elemList does is, it stores a map of raw function pointers which is mapped to an integer.

Additional: In order to assign a function to a function pointer, these things should match,

• The return type.
• Parameters of the function.
• The object which holds the function (this is only for member functions).