ptr_fun()

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A function adaptor that creates a function object from a pointer to a function

#include <functional>

namespace std {
  template<class Arg, class Result>
  pointer_to_unary_function<Arg, Result>
  ptr_fun(Result (*f)(Arg));

  template<class Arg1, class Arg2, class Result>
  pointer_to_binary_function<Arg1, Arg2, Result>
  ptr_fun(Result (*x)(Arg1, Arg2));
}

The pointer_to_unary_function and pointer_to_binary_function classes encapsulate pointers to functions, and use operator() so that the resulting object serves as a function object for the function.

The ptr_fun() function is overloaded to create instances of pointer_to_unary_function or pointer_to_binary_function when included with the appropriate pointer to a function.

//
//  pnt2fnct.cpp
//

#include <algorithm>    // for copy, transform
#include <functional>   // for ptr_fun
#include <iostream>     // cout, endl
#include <iterator>     // for ostream_iterator
#include <deque>        // for deque
#include <vector>       // for vector


int factorial (int x)
{
    return x > 1 ? x * factorial (x - 1) : x;
}


int main ()
{
    typedef std::deque<int, std::allocator<int> >  Deque;
    typedef std::vector<int, std::allocator<int> > Vector;
    typedef std::ostream_iterator<int, char, 
                                  std::char_traits<char> >
            Iter;

    // Initialize a deque with an array of integers.
    const Deque::value_type a[] = { 1, 2, 3, 4, 5, 6, 7 };
    Deque d (a + 0, a + sizeof a / sizeof *a);

    // Create an empty vector to store the factorials.
    Vector v (Vector::size_type (7));

    // Compute factorials of the contents of 'd' and 
    // store results in 'v'.
    std::transform (d.begin (), d.end (), v.begin (),
                    std::ptr_fun (factorial));

    // Print the results.
    std::cout << "The following numbers: \n     ";
    std::copy (d.begin (), d.end (), Iter (std::cout," "));

    std::cout << "\n\nHave the factorials: \n     ";
    std::copy (v.begin (), v.end (), Iter (std::cout, " "));
    std::cout << std::endl;

    return 0;
}


Program Output:

The following numbers: 
     1 2 3 4 5 6 7 

Have the factorials: 
     1 2 6 24 120 720 5040 

Function Objects, pointer_to_binary_function, pointer_to_unary_function, mem_fun

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 20.3.7