Defined in header <algorithm>  

(1)  
template< class RandomIt > RandomIt is_heap_until( RandomIt first, RandomIt last );  (since C++11) (until C++20)  
template< class RandomIt > constexpr RandomIt is_heap_until( RandomIt first, RandomIt last );  (since C++20)  
template< class ExecutionPolicy, class RandomIt > RandomIt is_heap_until( ExecutionPolicy&& policy, RandomIt first, RandomIt last );  (2)  (since C++17) 
(3)  
template< class RandomIt, class Compare > RandomIt is_heap_until( RandomIt first, RandomIt last, Compare comp );  (since C++11) (until C++20)  
template< class RandomIt, class Compare > constexpr RandomIt is_heap_until( RandomIt first, RandomIt last, Compare comp );  (since C++20)  
template< class ExecutionPolicy, class RandomIt, class Compare > RandomIt is_heap_until( ExecutionPolicy&& policy, RandomIt first, RandomIt last, Compare comp );  (4)  (since C++17) 
Examines the range [first, last)
and finds the largest range beginning at first
which is a max heap.
operator<
.comp
.policy
. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.first, last    the range of elements to examine 
policy    the execution policy to use. See execution policy for details. 
comp    comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than the second. The signature of the comparison function should be equivalent to the following:
While the signature does not need to have 
Type requirements  
RandomIt must meet the requirements of LegacyRandomAccessIterator. 
The upper bound of the largest range beginning at first
which is a max heap. That is, the last iterator it
for which range [first, it)
is a max heap.
Linear in the distance between first
and last
.
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
ExecutionPolicy
is one of the standard policies, std::terminate
is called. For any other ExecutionPolicy
, the behavior is implementationdefined. std::bad_alloc
is thrown. A max heap is a range of elements [f,l)
that has the following properties:
N = lf
, for all 0 < i < N
, f[(i1)/2]
does not compare less than f[i]
. std::push_heap
, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time. std::pop_heap
, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time. #include <iostream> #include <algorithm> #include <vector> int main() { std::vector<int> v { 3, 1, 4, 1, 5, 9 }; std::make_heap(v.begin(), v.end()); // probably mess up the heap v.push_back(2); v.push_back(6); auto heap_end = std::is_heap_until(v.begin(), v.end()); std::cout << "all of v: "; for (auto i : v) std::cout << i << ' '; std::cout << '\n'; std::cout << "only heap: "; for (auto i = v.begin(); i != heap_end; ++i) std::cout << *i << ' '; std::cout << '\n'; }
Output:
all of v: 9 5 4 1 1 3 2 6 only heap: 9 5 4 1 1 3 2
(C++11)  checks if the given range is a max heap (function template) 
creates a max heap out of a range of elements (function template) 

adds an element to a max heap (function template) 

removes the largest element from a max heap (function template) 

turns a max heap into a range of elements sorted in ascending order (function template) 

(C++20)  finds the largest subrange that is a max heap (niebloid) 
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