How to pass two parameters when using std::mem_fun?

Question

Lets say I have hierarchy like this (This is just a test program. Please do not point anything related to memory leaks, destructor is not virtual etc):

class I
{
public:
    virtual void fun(int n, int n1) = 0;
};

class A : public I
{
public:
    void fun(int n, int n1)
    {
        std::cout<<"A::fun():" <<n<<" and n1:" <<n1<<"\n";
    }
};

class B : public I
{
public:
    void fun(int n, int n1)
    {
        std::cout<<"B::fun():" <<n<<" and n1:" <<n1<<"\n";
    }
};


int  main()
{
    std::vector<I*> a;
    a.push_back(new A);
    a.push_back(new B);

    //I want to use std::for_each to call function fun with two arguments.
}

How do I call fun() method which takes two arguments using the std::for_each ? I think I have to use std::mem_fun probably with std::bind2nd but am not able to figure out how to do this. Any clue how to achieve this? I am not using boost.

Answer 1

You could create your own functor like this:

class Apply
{
private:
  int arg1, arg2;

public:
  Apply(int n, int n1)
    : arg1(n), arg2(n1) 
  {}        

  void operator() (I* pI) const
  {
    pI->fun(arg1, arg2);
  }
};

int main ()
{
  // ...
  std::for_each(a.begin(), a.end(), Apply(n, n1));
}

or use boost::bind like this:

std::for_each(
  a.begin(),
  a.end(),
  boost::bind(&I::fun, _1, n, n1));