std::is_heap
<algorithm>
bool is_heap( RandomIt first, RandomIt last );
(constexpr since C++20)
bool is_heap( ExecutionPolicy&& policy,
bool is_heap( RandomIt first, RandomIt last, Compare comp );
(constexpr since C++20)
bool is_heap( ExecutionPolicy&& policy,
Checks whether [
first,
last)
is a heap.
std::is_execution_policy_v <std::decay_t <ExecutionPolicy>> is true.
(until C++20)std::is_execution_policy_v <std::remove_cvref_t <ExecutionPolicy>> is true.
(since C++20)[edit] Parameters
The signature of the comparison function should be equivalent to the following:
bool cmp(const Type1& a, const Type2& b);
While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1
and Type2
regardless of value category (thus, Type1& is not allowed, nor is Type1 unless for Type1
a move is equivalent to a copy(since C++11)).
The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them.
RandomIt
must meet the requirements of LegacyRandomAccessIterator.
Compare
must meet the requirements of Compare.
[edit] Return value
true if the range is a heap with respect to the corresponding comparator, false otherwise.
[edit] Complexity
Given \(\scriptsize N\)N as std::distance (first, last):
[edit] Exceptions
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] Example
#include <algorithm> #include <bit> #include <iostream> #include <vector> int main() { std::vector <int> v{3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9}; std::cout << "initially, v:\n"; for (const auto& i : v) std::cout << i << ' '; std::cout << '\n'; if (!std::is_heap(v.begin(), v.end())) { std::cout << "making heap...\n"; std::make_heap (v.begin(), v.end()); } std::cout << "after make_heap, v:\n"; for (auto t{1U}; const auto& i : v) std::cout << i << (std::has_single_bit (++t) ? " | " : " "); std::cout << '\n'; }
Output:
initially, v: 3 1 4 1 5 9 2 6 5 3 5 8 9 7 9 making heap... after make_heap, v: 9 | 6 9 | 5 5 9 7 | 1 1 3 5 8 3 4 2 |