How to call a pointer to method from another method

Question

I had this problem some time ago and I gave up but lately it returned.

#include <iostream>

class element2D;

class node2D
{
public:
    void (element2D::*FunctionPtr)();
    void otherMethod()
    { std::cout << "hello" << std::endl;
        ((this)->*(this->FunctionPtr))(); //ERROR<-------------------
    }

};

class element2D
{
public:
    node2D myNode;
    void doSomething(){ std::cout << "do something" << std::endl; }
};

int main()
{
    element2D myElement;

    myElement.myNode.FunctionPtr = &element2D::doSomething; //OK
    ((myElement).*(myElement.myNode.FunctionPtr))();        //OK

    return 0;
}

I'm getting error at marked line:

pointer to member type 'void (element2D::)()' incompatible with object type 'node2D'

I would be really thankful for help. There was similar question today which partially helped me: link. But it doesn't seem to be the full answer to my problem.

Actually these two problems have only one difference - point where the function is called.

Thanks for your time

Answer 1

You need a pointer to element2D object if you wish to call a pointer to element2D member. Consider using Boost.Function or Boost.Signals2 for the functionality that you want.

Answer 2

"this" is a pointer to node2D but FunctionPtr refers to a member of element2D -- that is the error.

#if 0 // broken version

void otherMethod()
{ std::cout << "hello" << std::endl;
    ((this)->*(this->FunctionPtr))(); //ERROR<-------------------
}

#else // fixed version

void otherMethod( element2D * that )
{ std::cout << "hello" << std::endl;
    ((that)->*(this->FunctionPtr))();
}

#endif

Then you call it with something like:

myElement.myNode.otherMethod( &myElement );

There are things you could do to improve on this, but this should get you started.