Re: std::binary_function

std::for_each allows you to iterate over range of type T and apply a
unary (one argument) function object or function pointer to each
element in the range. The argument of this function is of type R where
T is convertible to R ( ie R is probably T, const T, T& or const T& )

for example:

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

struct average : public std::unary_function<double,void>
{
  double sum_;
  long count_;

  average() : sum_(0), count_(0) {}
  void operator()(double value){ sum_ += value; ++count_; }
  operator double () { return double( sum_ / count_ ); }
};

int main() {
  using namespace std;
  std::vector<double> v;

  for(int i = 1; i != 11; ++i ) { v.push_back(i); }
  cout << for_each( v.begin(), v.end(), average() ) << endl;

  return 0;
}

outputs 5.5

It is not possible to pass in a second argument to for_each because it
requires a unary function, although you can bind an argument to a
binary function (this all gets rather complicated). To get around this
you may want to write a function object wrapper.

To be honest, if you don't know what for_each does or what a function
object is then you should probably get to grips with them before
trying fancy stuff.

Good luck,
Brian