# std::sort_heap

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class RandomIt > void sort_heap( RandomIt first, RandomIt last ); | (1) | (constexpr since C++20)
template< class RandomIt, class Compare > void sort_heap( RandomIt first, RandomIt last, Compare comp ); | (2) | (constexpr since C++20)

Converts the heap `[`first`,` last`)` into a sorted range. The heap property is no longer maintained.

1) The heap is with respect to operator<(until C++20) std::less {}(since C++20), and will be sorted with respect to operator<(until C++20) std::less {}(since C++20).
2) The heap is with respect to comp, and will be sorted with respect to comp.

If any of the following conditions is satisfied, the behavior is undefined:

- `[`first`,` last`)` is not a heap.

- The type of *first is not Swappable.

(until C++11)

- `RandomIt` is not ValueSwappable.
- The type of *first is not MoveConstructible.
- The type of *first is not MoveAssignable.

(since C++11)

### Parameters

first, last | - | the heap to be sorted

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:

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.

Type requirements
- `RandomIt` must meet the requirements of LegacyRandomAccessIterator.
- `Compare` must meet the requirements of Compare.

### Complexity

Given \(\scriptsize N\)N as std::distance (first, last):

1) At most \(\scriptsize 2N \cdot \log(N)\)2N⋅log(N) comparisons using operator<(until C++20) std::less {}(since C++20).
2) At most \(\scriptsize 2N \cdot \log(N)\)2N⋅log(N) applications of the comparison function comp.

### Possible implementation

sort_heap (1)

    template<class RandomIt>
    void sort_heap(RandomIt first, RandomIt last)
    {
        while (first != last)
            std::pop_heap(first, last--);
    }

sort_heap (2)

    template<class RandomIt, class Compare>
    void sort_heap(RandomIt first, RandomIt last, Compare comp)
    {
        while (first != last)
            std::pop_heap(first, last--, comp);
    }

### Example

Run this code

    #include <algorithm>
    #include <iostream>
    #include <string_view>
    #include <vector>

    void println(std::string_view fmt, const auto& v)
    {
        for (std::cout << fmt; const auto &i : v)
            std::cout << i << ' ';
        std::cout << '\n';
    }

    int main()
    {
        std::vector<int> v{3, 1, 4, 1, 5, 9};

        std::make_heap(v.begin(), v.end());
        println("after make_heap, v: ", v);

        std::sort_heap(v.begin(), v.end());
        println("after sort_heap, v: ", v);
    }

Output:

    after make_heap, v: 9 4 5 1 1 3
    after sort_heap, v: 1 1 3 4 5 9

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2444 | C++98 | at most \(\scriptsize N \cdot \log(N)\)N⋅log(N) comparisons were allowed | increased to \(\scriptsize 2N \cdot \log(N)\)2N⋅log(N)

### See also

is_heap (C++11) | checks if the given range is a max heap (function template)
is_heap_until (C++11) | finds the largest subrange that is a max heap (function template)
make_heap | creates a max heap out of a range of elements (function template)
pop_heap | removes the largest element from a max heap (function template)
push_heap | adds an element to a max heap (function template)
ranges::sort_heap (C++20) | turns a max heap into a range of elements sorted in ascending order (algorithm function object)

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