ptr_fun

Function Adaptor

Summary
Data Type and Member Function Indexes
Synopsis
Description
Example
Warnings
See Also

Summary

A function that is overloaded to adapt a pointer to a function, to take the place of a function.

Data Type and Member Function Indexes
(exclusive of constructors and destructors)

None

Synopsis

#include <functional>
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));

Description

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.

Example

//
// pnt2fnct.cpp
//
 #include <functional>
 #include <deque>
 #include <vector>
 #include <algorithm>
 #include <iostream>
 using namespace std;

 //Create a function
 int factorial(int x)
 {
   int result = 1;
   for(int i = 2; i <= x; i++)
       result *= i;
   return result;
 }

 int main()
 {
   //Initialize a deque with an array of ints
   int init[7] = {1,2,3,4,5,6,7};
   deque<int> d(init, init+7);

   //Create an empty vector to store the factorials
   vector<int> v((size_t)7);

   //Transform the numbers in the deque to their 
   //factorials and store in the vector
   transform(d.begin(), d.end(), v.begin(),
             ptr_fun(factorial));

   //Print the results
   cout << "The following numbers: " << endl << "     ";
   copy(d.begin(),d.end(),
        ostream_iterator<int,char>(cout," "));

   cout << endl << endl;
   cout << "Have the factorials: " << endl << "     ";
   copy(v.begin(),v.end(),
        ostream_iterator<int,char>(cout," "));

   return 0;
 }

Program Output

The following numbers:
     1 2 3 4 5 6 7
Have the factorials:
     1 2 6 24 120 720 5040

Warnings

If your compiler does not support default template parameters, you always need to supply the Allocator template argument. For instance, you need to write:

vector<int, allocator<int> >

instead of:

vector<int>

If your compiler does not support namespaces, then you do not need the using declaration for std.