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map::value_comp

The member function returns a function object that determines the order of elements in a map by comparing their key values.

value_compare value_comp( ) const;

Returns the comparison function object that a map uses to order its elements.

For a map m, if two elements e1(k1, d1) and e2(k2, d2) are objects of type value_type, where k1 and k2 are their keys of type key_type and d1 and d2 are their data of type mapped_type, then m.value_comp(e1, e2) is equivalent to m.key_comp(k1, k2). A stored object defines the member function

bool operator(value_type& _Left, value_type& _Right);

which returns true if the key value of _Left precedes and is not equal to the key value of _Right in the sort order.

// map_value_comp.cpp
// compile with: /EHsc
#include <map>
#include <iostream>

int main( )
{
   using namespace std;
   
   map <int, int, less<int> > m1;
   map <int, int, less<int> >::value_compare vc1 = m1.value_comp( );
   pair< map<int,int>::iterator, bool > pr1, pr2;
   
   pr1= m1.insert ( map <int, int> :: value_type ( 1, 10 ) );
   pr2= m1.insert ( map <int, int> :: value_type ( 2, 5 ) );

   if( vc1( *pr1.first, *pr2.first ) == true )   
   {
      cout << "The element ( 1,10 ) precedes the element ( 2,5 )."
           << endl;
   }
   else   
   {
      cout << "The element ( 1,10 ) does not precede the element ( 2,5 )."
           << endl;
   }

   if(vc1( *pr2.first, *pr1.first ) == true )
   {
      cout << "The element ( 2,5 ) precedes the element ( 1,10 )."
           << endl;
   }
   else   
   {
      cout << "The element ( 2,5 ) does not precede the element ( 1,10 )."
           << endl;
   }
}
The element ( 1,10 ) precedes the element ( 2,5 ).
The element ( 2,5 ) does not precede the element ( 1,10 ).

Header: <map>

Namespace: std

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