ptr_fun

#include <functional>
namespace std {
    template < class Arg, class Result >
    pointer_to_unary_function < Arg, Result > ptr_fun( Result( * f )( Arg ) )
    {
        return pointer_to_unary_function < Arg, Result >( f );
    }
   
    template < class Arg1, class Arg2, class Result >
    pointer_to_binary_function < Arg1, Arg2, Result > ptr_fun( Result( * f )( Arg1, Arg2 ) )
    {
        return pointer_to_binary_function < Arg1, Arg2, Result >( f );
    }
}

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

bool less_5( int a ) {
    return a < 5;
}

int main() {
    int tab[ 5 ] = { 1, 3, 6, 10, - 1 };
    std::cout << "Liczby: ";
    for( int a = 0; a < 5; ++a ) std::cout << tab[ a ] << " ";
   
    std::cout << std::endl;
    std::cout << "W zbiorze sa " << std::count_if( tab, tab + 5, std::ptr_fun( less_5 ) ) << " liczby mniejsze niz 5." << std::endl;
}