hash_map::difference_type
A signed integer type that can be used to represent the number of elements of a hash_map in a range between elements pointed to by iterators.
typedef list<typename _Traits::value_type, typename _Traits::allocator_type>::difference_type difference_type;
Remark
The difference_type is the type returned when subtracting or incrementing through iterators of the container. The difference_type is typically used to represent the number of elements in the range [_First, _Last) between the iterators _First and _Last, includes the element pointed to by _First and the range of elements up to, but not including, the element pointed to by _Last.
Note that although difference_type is available for all iterators that satisfy the requirements of an input iterator, which includes the class of bidirectional iterators supported by reversible containers such as set, subtraction between iterators is only supported by random-access iterators provided by a random access container, such as vector.
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_diff_type.cpp
// compile with: /EHsc
#define _DEFINE_DEPRECATED_HASH_CLASSES 0
#include <iostream>
#include <hash_map>
#include <algorithm>
int main( )
{
using namespace std;
using namespace stdext;
hash_map <int, int> hm1;
typedef pair <int, int> Int_Pair;
hm1.insert ( Int_Pair ( 2, 20 ) );
hm1.insert ( Int_Pair ( 1, 10 ) );
hm1.insert ( Int_Pair ( 3, 20 ) );
// The following won't insert, because map keys are unique
hm1.insert ( Int_Pair ( 2, 30 ) );
hash_map <int, int>::iterator hm1_Iter, hm1_bIter, hm1_eIter;
hm1_bIter = hm1.begin( );
hm1_eIter = hm1.end( );
// Count the number of elements in a hash_map
hash_map <int, int>::difference_type df_count = 0;
hm1_Iter = hm1.begin( );
while ( hm1_Iter != hm1_eIter)
{
df_count++;
hm1_Iter++;
}
cout << "The number of elements in the hash_map hm1 is: "
<< df_count << "." << endl;
cout << "The keys of the mapped elements are:";
for ( hm1_Iter= hm1.begin( ) ; hm1_Iter!= hm1.end( ) ;
hm1_Iter+)
cout << " " << hm1_Iter-> first;
cout << "." << endl;
cout << "The values of the mapped elements are:";
for ( hm1_Iter= hm1.begin( ) ; hm1_Iter!= hm1.end( ) ;
hm1_Iter+)
cout << " " << hm1_Iter-> second;
cout << "." << endl;
}
The number of elements in the hash_map hm1 is: 3. The keys of the mapped elements are: 1 2 3. The values of the mapped elements are: 10 20 20.
Requirements
Header: <hash_map>
Namespace: stdext