How to use the pair logical operator Standard Template Library (STL) functions in Visual C++ (157670)

MORE INFORMATION

Required header

   < utility >

Prototype

It is interesting to note that only the < and == operators are necessary in order to define all of the logical operators.

   template<class _T1, class _T2> inline

      bool operator==(const pair<_T1, _T2>& _X,
         const pair<_T1, _T2>& _Y)
      {return (_X.first == _Y.first && _X.second == _Y.second); }

   template<class _T1, class _T2> inline

      bool operator<(const pair<_T1, _T2>& _X,
         const pair<_T1, _T2>& _Y)
      {return (_X.first < _Y.first ||
         !(_Y.first < _X.first) && _X.second < _Y.second); }

Note The class/parameter names in the prototype may not match the version in the header file. Some have been modified to improve readability.

Description

The functions are described in the comments section of the sample.

Sample code

///////////////////////////// 
// Compile options needed: none
// 
// paircomp.cpp : Illustrates several comparison
//                operators used to compare two
//                pair objects.
// 
// Functions:
// 
//    operator== - returns true if two pair objects are identical.
// 
//    operator!= - returns true if two pair objects are not identical.
// 
//    operator<  - returns true for (A < B) if pair object A is less
//                 than pair object B.
// 
//    operator<= - returns true for (A <= B) if pair object A is less
//                 than or equal to pair object B.
// 
//    operator>  - returns true for (A > B) if pair object A is greater
//                 than pair object B.
// 
//    operator>= - returns true for (A >= B) if pair object A is greater
//                 than or equal to pair object B.
// 
// Written by Mark Hagen
// of Microsoft Technical Support
// Copyright (c) 1996 Microsoft Corporation.
// All rights reserved.
///////////////////////////// 

#include <iostream>
#include <utility>

#if _MSC_VER > 1020   // if VC++ version is > 4.2
   using namespace std;  // std c++ libs implemented in std
   #endif

/* STL pair data type containing int and float */ 

typedef struct pair<int, float> PAIR_IF;

void main(void)

{
  PAIR_IF A(10,3.14);
  PAIR_IF B(18,3.14);
  PAIR_IF C(10,6.28);
  PAIR_IF D(10,3.14);

/* show pair values */ 

  cout << "A = ( " << A.first << " , " << A.second << " )" << endl;
  cout << "B = ( " << B.first << " , " << B.second << " )" << endl;
  cout << "C = ( " << C.first << " , " << C.second << " )" << endl;
  cout << "D = ( " << D.first << " , " << D.second << " )" << endl;

/* operator== */ 

  if (A==D)

    cout << "A and D are equal" << endl;

  else

    cout << "A and D are not equal" << endl;

/* operator!= */ 

  if (B!=C)

    cout << "B and C are not equivalent" << endl;

  else

    cout << "B and C are equivalent" << endl;

/* operator> */ 

  if (A>C)

    cout << "A is greater than C" << endl;

  else

    cout << "A is not greater than C" << endl;

/* operator>= */ 

  if (A>=C)

    cout << "A is greater than or equal to C" << endl;

  else

    cout << "A is not greater than or equal to C" << endl;

/* operator< */ 

  if (C<D)

    cout << "C is less than D" << endl;

  else

    cout << "C is not less than D" << endl;

/* operator<= */ 

  if (C<D)

    cout << "C is less than or equal to D" << endl;

  else

    cout << "C is not less than or equal to D" << endl;

}

Program Output is:

A = ( 10 , 3.14 )
B = ( 18 , 3.14 )
C = ( 10 , 6.28 )
D = ( 10 , 3.14 )
A and D are equal
B and C are not equivalent
A is not greater than C
A is not greater than or equal to C
C is not less than D
C is not less than or equal to D