CODEWITHSUNDEEP
c++boost
Frysen
Frysen

Reputation: 7

Function pointers to object instance returned by function pointer

Im new to c++. I want to make a std::map with strings of get-method names mapped their respective get-method. These are to be looped over and present the value obtained by the get-methodtogether with the method name. I will loop over several instances of the type A. I have found that boost/function is very useful for storing the get-methods in A. However, A also has an instance of type B, with its own get-methods. How do I access the get-method in B?

Here is my current code (The line mapping["B_Nine"] = &B::(&A::getB)::nine is wrong, but my best guess so far)...

#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <boost/ref.hpp>
#include <iostream>
#include <map>
#include <string>
#include <functional>

class B
{
public:
    B();
    ~B();
    int nine() {return 9;}
};

B::B()
{

}

B::~B()
{

}

class A 
{
public:
    A();
    ~A();
   int one () {return 1;}
   int two () {return 2;}
   B getB() {return b;}
   B b;
};

A::A()
{   
   b = B();
}

A::~A()
{

}


typedef std::map<std::string,boost::function<int (A*)>> str_func_map;

int main()
{

    str_func_map mapping;

    mapping["One"] = &A::one;
    mapping["Two"] = &A::two;
     mapping["B_Nine"] = &B::(&A::getB)::nine //This line is wrong - how should 
                                              //it be done correctly??

    A* a = new A();

    for (str_func_map::iterator i = mapping.begin(); i != mapping.end(); i++)
    {
        std::cout<< i->first << std::endl;
        std::cout<< (i->second)(a) << std::endl;
    }

    system("pause");
}

Upvotes: 1

Views: 81

Answers (1)

Maciej Chałapuk
Maciej Chałapuk

Reputation: 462

// free function
int callMethodOfB(A *a, std::function<int(B*)> method) {
   return method(&(a->getB()));
}

mapping["B_Nine"] = std::bind<int>(&callMethodOfB, std:placeholder::_1, &B::nine);

or

mapping["B_Nine"] = [] (A *a) { return a->getB().nine(); }

Upvotes: 3

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