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c++functionc++11pointers
user1453817
user1453817

Reputation: 87

c++ pointer to member function using std::function

I know this has been asked multiple times, most of the answers are difficult for me to understand. Could you please help me in figuring out what am I doing wrong ?

#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>
#include <functional>

class A{
    public:
        A(double i){
            _b = i;
        }
        double square(double i){

            return i*i*_b;
        }


    private:
    double _i;
    double _b;
};

double cube(double (*objfunc)(double), double x){
    return objfunc(x)*x;   
}

int main()
{
    double v = 2.0;
    A a(v);

    using std::placeholders::_1;
    std::function<double(double)> f_square = std::bind( &A::square, &a, _1 );
    double x = cube(f_square,3.0);
    std::cout << " x = " << x << std::endl;


}

Thank you as always for your advice.

Given the class A and the cube function as they are how can I use the cube function in the main function ?

Update: Only way to do this would be to modify:

double cube(std::function<double(double)> objfunc, double x){
    return objfunc(x)*x;   
}

Upvotes: 0

Views: 72

Answers (1)

Henri Menke
Henri Menke

Reputation: 10939

Make cube take an std::function object instead of a function pointer. Also get rid of the std::bind and use a lambda together with the magic of auto.

#include <iostream>
#include <functional>

class A
{
public:
  A(double i) : _b(i) {}
  double square(double i) { return i*i*_b; }
private:
  double _b;
};

double cube(std::function<double(double)> objfunc, double x)
{
  return objfunc(x)*x;   
}

int main()
{
  double v = 2.0;
  A a(v);

  auto f_square = [&a] ( double x ) { return a.square(x); };
  double x = cube(f_square,3.0);
  std::cout << " x = " << x << std::endl;
}

Upvotes: 2

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