Function Adaptor
A function that is overloaded to adapt a pointer to a function to work where a function is called for.
#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));
The pointer_to_unary_function and pointer_to_binary_function classes encapsulate pointers to functions and provide an 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 provided with the appropriate pointer to a function.
//
// pnt2fnct.cpp
//
#include <functional>
#include <deque>
#include <vector>
#include <algorithm>
#include <iostream.h>
//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>(cout," "));
cout << endl << endl;
cout << "Have the factorials: " << endl << " ";
copy(v.begin(),v.end(),ostream_iterator<int>(cout," "));
return 0;
}
Output :
The following numbers:
1 2 3 4 5 6 7
Have the factorials:
1 2 6 24 120 720 5040
If your compiler does not support default template parameters, you need to always supply the Allocator template argument. For instance, you will need to write :
vector<int, allocator>
instead of :
vector<int>
Function Objects, pointer_to_binary_function, pointer_to_unary_function