<algorithm>
template <class InputIterator, class T>
typename iterator_traits<InputIterator>::difference_type
count ( ForwardIterator first, ForwardIterator last, const T& value );
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:
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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;
}
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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.
value
- Value to compare the elements in the range with.
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
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// 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;
}
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Output:
10 appears 3 times.
20 appears 3 times.
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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) |
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