template <class InputIterator, class T>
typename iterator_traits<InputIterator>::difference_type
count ( ForwardIterator first, ForwardIterator last, const T& value ); |
<algorithm> |
Count appearances of value in range
Returns the number of elements in the range [first,last) that compare equal to value.
The behavior of this function template is equivalent to:
template <class InputIterator, class T>
ptrdiff_t count ( InputIterator first, InputIterator last, const T& value )
{
ptrdiff_t ret=0;
while (first != last) if (*first++ == value) ++ret;
return ret;
}
|
Parameters
- first, last
- Forward iterators to the initial and final positions of the sequence of elements. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
Return value
The number of elements in the range
[first,last) that compare equal to
value.
The return type (
iterator_traits<InputIterator>::difference_type) is a signed integral type, generally defined as the same type as
ptrdiff_t.
Example
// count algorithm example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main () {
int mycount;
// counting elements in array:
int myints[] = {10,20,30,30,20,10,10,20}; // 8 elements
mycount = (int) count (myints, myints+8, 10);
cout << "10 appears " << mycount << " times.\n";
// counting elements in container:
vector<int> myvector (myints, myints+8);
mycount = (int) count (myvector.begin(), myvector.end(), 20);
cout << "20 appears " << mycount << " times.\n";
return 0;
}
|
Output:
10 appears 3 times.
20 appears 3 times.
|
Complexity
Linear: Performs as many comparisons as the number of elements between
first and
last.
See also
| for_each | Apply function to range (template function) |
| count_if | Return number of elements in range satisfying condition (function template) |
| find | Find value in range (function template) |
| replace | Replace value in range (function template) |
