std::partition_point

Defined in header <algorithm>

template< class ForwardIt, class UnaryPredicate >
ForwardIt partition_point( ForwardIt first, ForwardIt last, UnaryPredicate p );

(1)

(since C++11)

Examines the partitioned (as if by std::partition) range [first, last) and locates the end of the first partition, that is, the first element that does not satisfy p or last if all elements satisfy p.

Parameters

first, last	-	the partitioned range of elements to examine
p	-	unary predicate which returns `true` for the elements found in the beginning of the range. The signature of the predicate function should be equivalent to the following: `bool pred(const Type &a);` The signature does not need to have `const &`, but the function must not modify the objects passed to it. The type `Type` must be such that an object of type `ForwardIt` can be dereferenced and then implicitly converted to `Type`.
Type requirements
- `ForwardIt` must meet the requirements of `ForwardIterator`.
- `UnaryPredicate` must meet the requirements of `Predicate`.

Return value

The iterator past the end of the first partition within [first, last) or last if all elements satisfy p.

Complexity

The number of applications of the predicate p is logarithmic in the distance between first and last.

Example

#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
  
int main()
{
    std::array<int, 9> v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
  
    auto is_even = [](int i){ return i % 2 == 0; };
    std::partition(v.begin(), v.end(), is_even);
  
    auto p = std::partition_point(v.begin(), v.end(), is_even);
  
    std::cout << "Before partition:\n    ";
    std::copy(v.begin(), p, std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\nAfter partition:\n    ";
    std::copy(p, v.end(), std::ostream_iterator<int>(std::cout, " "));
}

Output:

Before partition:
    8 2 6 4 
After partition:
    5 3 7 1 9

std::partition_point

Parameters

Return value

Complexity

Example

See also