hash_map::count
Returns the number of elements in a hash_map whose key matches a parameter-specified key.
size_type count(
const Key& _Key
) const;
Parameters
- _Key
The key value of the elements to be matched from the hash_map.
Return Value
1 if the hash_map contains an element whose sort key matches the parameter key; 0 if the hash_map doesn't contain an element with a matching key.
Remarks
The member function returns the number of elements x in the range
[lower_bound (_Key ), upper_bound (_Key ) )
which is 0 or 1 in the case of hash_map, which is a unique associative container.
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
When compiling this example with the /Wp64 flag or on a 64-bit platform, compiler warning C4267 will be generated. For more information on this warning, see Compiler Warning (level 3) C4267.
// hash_map_count.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> hm1;
hash_map<int, int>::size_type i;
typedef pair<int, int> Int_Pair;
hm1.insert(Int_Pair (1, 1));
hm1.insert(Int_Pair (2, 1));
hm1.insert(Int_Pair (1, 4));
hm1.insert(Int_Pair (2, 1));
// Keys must be unique in hash_map, so duplicates are ignored
i = hm1.count(1);
cout << "The number of elements in hm1 with a sort key of 1 is: "
<< i << "." << endl;
i = hm1.count(2);
cout << "The number of elements in hm1 with a sort key of 2 is: "
<< i << "." << endl;
i = hm1.count(3);
cout << "The number of elements in hm1 with a sort key of 3 is: "
<< i << "." << endl;
}
The number of elements in hm1 with a sort key of 1 is: 1. The number of elements in hm1 with a sort key of 2 is: 1. The number of elements in hm1 with a sort key of 3 is: 0.
Requirements
Header: <hash_map>
Namespace: stdext