map::count
public member function
size_type count ( const key_type& x ) const;
Count elements with a specific key
Searches the container for an element with a key of x and returns the number of elements having that key. Because map containers do not allow for duplicate keys, this means that the function actually returns 1 if an element with that key is found, and zero otherwise.
Parameters
- x
- Key value to be searched for.
key_type is a member type defined in map containers as an alias of Key, which is the first template parameter and the type of the keys for the elements stored in the container.
Return value
1 if an element with a key equivalent to x is found, or zero otherwise.
Member type size_type is an unsigned integral type.
Example
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
|
// map::count
#include <iostream>
#include <map>
using namespace std;
int main ()
{
map<char,int> mymap;
char c;
mymap ['a']=101;
mymap ['c']=202;
mymap ['f']=303;
for (c='a'; c<'h'; c++)
{
cout << c;
if (mymap.count(c)>0)
cout << " is an element of mymap.\n";
else
cout << " is not an element of mymap.\n";
}
return 0;
}
|
Output:
a is an element of mymap.
b is not an element of mymap.
c is an element of mymap.
d is not an element of mymap.
e is not an element of mymap.
f is an element of mymap.
g is not an element of mymap.
|
Complexity
Logarithmic in size.
See also
| map::find | Get iterator to element (public member function) |
| map::size | Return container size (public member function) |
|