count_if
Returns the number of elements in a range whose values satisfy a specified condition.
template<class InputIterator, class Predicate>
typename iterator_traits<InputIterator>::difference_type count_if(
InputIterator _First,
InputIterator _Last,
Predicate _Pred
);
Parameters
_First
An input iterator addressing the position of the first element in the range to be searched._Last
An input iterator addressing the position one past the final element in the range to be searched._Pred
User-defined predicate function object that defines the condition to be satisfied if an element is to be counted. A predicate takes single argument and returns true or false.
Return Value
The number of elements that satisfy the condition specified by the predicate.
Remarks
This template function is a generalization of the algorithm count, replacing the predicate "equals a specific value" with any predicate.
Example
// alg_count_if.cpp
// compile with: /EHsc
#include <vector>
#include <algorithm>
#include <iostream>
bool greater10(int value)
{
return value >10;
}
int main()
{
using namespace std;
vector<int> v1;
vector<int>::iterator Iter;
v1.push_back(10);
v1.push_back(20);
v1.push_back(10);
v1.push_back(40);
v1.push_back(10);
cout << "v1 = ( ";
for (Iter = v1.begin(); Iter != v1.end(); Iter++)
cout << *Iter << " ";
cout << ")" << endl;
vector<int>::iterator::difference_type result1;
result1 = count_if(v1.begin(), v1.end(), greater10);
cout << "The number of elements in v1 greater than 10 is: "
<< result1 << "." << endl;
}
v1 = ( 10 20 10 40 10 )
The number of elements in v1 greater than 10 is: 2.
Requirements
Header: <algorithm>
Namespace: std