Convenience function for the compose_f_gx_hy adapter : predicate « STL Introduction « C++ Tutorial

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2. STL Introduction
3. predicate

/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
#include <cctype>

using namespace std;


#include <functional>

/* class for the compose_f_gx_hy adapter
 */
template <class OP1, class OP2, class OP3>
class compose_f_gx_hy_t
 : public std::binary_function<typename OP2::argument_type,
                               typename OP3::argument_type,
                               typename OP1::result_type>
{
  private:
    OP1 op1;    // process: op1(op2(x),op3(y))
    OP2 op2;
    OP3 op3;
  public:
    // constructor
    compose_f_gx_hy_t (const OP1& o1, const OP2& o2, const OP3& o3)
     : op1(o1), op2(o2), op3(o3) {
    }

    // function call
    typename OP1::result_type
    operator()(const typename OP2::argument_type& x,
               const typename OP3::argument_type& y) const {
        return op1(op2(x),op3(y));
    }
};

/* convenience function for the compose_f_gx_hy adapter
 */
template <class OP1, class OP2, class OP3>
inline compose_f_gx_hy_t<OP1,OP2,OP3>
compose_f_gx_hy (const OP1& o1, const OP2& o2, const OP3& o3) {
    return compose_f_gx_hy_t<OP1,OP2,OP3>(o1,o2,o3);
}


int main()
{
    string s("Internationalization");
    string sub("Nation");

    // search substring case insensitive
    string::iterator pos;
    pos = search (s.begin(),s.end(),           // string to search in
                  sub.begin(),sub.end(),       // substring to search
                  compose_f_gx_hy(equal_to<int>(), // compar. criterion
                                  ptr_fun(::toupper),
                                  ptr_fun(::toupper)));

    if (pos != s.end()) {
        cout << "\"" << sub << "\" is part of \"" << s << "\""
             << endl;
    }
}

"Nation" is part of "Internationalization"