How to assign to the array of pointers functions from another object?

Question

I defined

int(*Functions[3])();

int select(){
cout<<"SELECT!";
getchar();
}

Now i want to assign a function to 'Functions', and when i do like this:

Functions[0]=select;
Functions[0];

It works, but i want to assign function 'select' from my own object

class worker{
HERE DEFINED FUNCTION
}

worker object1;
Functions[0]=object1.select;

It doesn't work. "use '&' to create a pointer to member", " '=':cannot convert from 'int(_thiscall worker::)(void)' to 'int(_cdecl)(void)'"

I don't know a differences between using

select();
object1.select();

A pointer to non-member function cannot be used for it.

Raindrop7
– Raindrop7

2018-03-18 23:34:31 +00:00
Commented Mar 18, 2018 at 23:34 — Raindrop7
– Raindrop7, Commented Mar 18, 2018 at 23:34
Why not? Can you explain?

Artur Szczypta
– Artur Szczypta

2018-03-18 23:36:59 +00:00
Commented Mar 18, 2018 at 23:36 — Artur Szczypta
– Artur Szczypta, Commented Mar 18, 2018 at 23:36
can you use a pointer to int to point to a string?

Raindrop7
– Raindrop7

2018-03-18 23:43:37 +00:00
Commented Mar 18, 2018 at 23:43 — Raindrop7
– Raindrop7, Commented Mar 18, 2018 at 23:43

Raindrop7 · Accepted Answer · 2018-03-18 23:56:37Z

1

A pointer to member function cannot be used for a non-member function and vice-versa. If you want then create another one for a member function in your example.

class Foo{
    public:
        void func(){
            cout << "Foo::func()" << endl;
        }
};

void func2(){
    cout << "func2()" << endl;
}


int main(){

    void(*pFunc[3])();
    pFunc[0] = func2;

    void(Foo::*pFunc2[3])();
    pFunc2[0] = &Foo::func;

    Foo theFoo; // You need an object to call it
    (theFoo.*(pFunc2[0]))(); // calling the member function

    return 0;
}

In addition as @Serge's useful comment:

pointer to a member function requires knowledge of a type of the encapsulating object and an instance of an object at the time it is used. Therefore it is not a simple pointer which you can use for static function only (including static function defined within a class).

edited Mar 18, 2018 at 23:56

answered Mar 18, 2018 at 23:40

Raindrop7

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8 Comments

Serge Over a year ago

pointer to a member function requires knowledge of a type of the encapsulating object and an instance of an object at the time it is used. Therefore it is not a simple pointer. The simple pointer you can use for static function only (including static function defined within a class). The latter might be just an address of the function in the memory.

Artur Szczypta Over a year ago

It works, but one more question, how to call this function?

Raindrop7 Over a year ago

@Serge: Thank you for your useful comment.

Raindrop7 Over a year ago

void print( void(Foo::*pFunc[])(), int size ){ Foo f; for(int i(0); i != size; ++i) (f.*pFunc[i])(); }

Raindrop7 Over a year ago

you can also pass the object f to function not just declaring it inside the function.

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