hash_map::value_comp
Returns a function object that determines the order of elements in a hash_map by comparing their key values.
value_compare value_comp( ) const;
Return Value
Returns the comparison function object that a hash_map uses to order its elements.
Remarks
For a hash_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.
In Visual C++ .NET 2003, members of the <hash_map> and <hash_set> header files are no longer in the std namespace, but rather have been moved into the stdext namespace. See The stdext Namespace for more information.
Example
// hash_map_value_comp.cpp
// compile with: /EHsc
#define _DEFINE_DEPRECATED_HASH_CLASSES 0
#include <hash_map>
#include <iostream>
int main( )
{
using namespace std;
using namespace stdext;
hash_map <int, int, hash_compare<int, less<int> > > hm1;
hash_map <int, int, hash_compare<int, less<int> > >
::value_compare vc1 = hm1.value_comp( );
pair< hash_map<int,int>::iterator, bool > pr1, pr2;
pr1= hm1.insert ( hash_map <int, int> :: value_type ( 1, 10 ) );
pr2= hm1.insert ( hash_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;
}
}
Output
The element ( 1,10 ) precedes the element ( 2,5 ).
The element ( 2,5 ) does not precede the element ( 1,10 ).
Requirements
Header: <hash_map>
Namespace: stdext