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Pair Logical Operator 

Illustrates how to use the pair logical operator Standard Template Library (STL) function in Visual C++.

NoteNote

Only operator< and operator== are necessary 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
   ); }

NoteNote

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

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

// paircomp.cpp
// compile with: /EHsc
// 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.
/////////////////////////////

#include <iostream>
#include <utility>

using namespace std ;

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

typedef struct pair<int, float> PAIR_IF;

int main(void)
{
  PAIR_IF A(10,3.14f);
  PAIR_IF B(18,3.14f);
  PAIR_IF C(10,6.28f);
  PAIR_IF D(10,3.14f);

/* 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;
}

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

Header: <utility>

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