std::sort_heap

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

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 The heap property is no longer maintained.

1) [first, last) is a heap with respect to operator<, and will be sorted with respect to operator<.

2) [first, last) is a heap with respect to comp, and will be sorted with respect to comp.

If [first, last) is not a heap, the behavior is undefined.

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 ValueSwappable and LegacyRandomAccessIterator.
- The type of dereferenced `RandomIt` must meet the requirements of MoveAssignable and MoveConstructible.
- `Compare` must meet the requirements of Compare.

Return value

(none)

Complexity

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

1) At most

2N\cdotlog(N)

comparisons using operator<.

2) At most

2N\cdotlog(N)

applications of the comparison function comp.

Notes

A heap with respect to comp (max heap) is a random access range [first, last) that has the following properties:

Given $\scriptsize N$ $N$ as last - first, for all integer i where $\scriptsize 0 < i < N$ $0 < i < N$ , bool(comp(first[(i - 1) / 2], first[i])) is false.
A new element can be added using std::push_heap, in $\scriptsize \mathcal{O}(\log N)$ $𝓞(log N)$ time.
*first can be removed using std::pop_heap, in $\scriptsize \mathcal{O}(\log N)$ $𝓞(log N)$ time.

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, auto const& 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 193	C++98	heap required *first to be the largest element	there can be elements equal to *first
LWG 2166	C++98	the heap reqirement did not match the definition of max heap closely enough	requirement imporved
LWG 2444	C++98	at most $\scriptsize N \cdot log(N)$ $N\cdotlog(N)$ comparisons were allowed	increased to $\scriptsize 2N \cdot log(N)$ $2N\cdotlog(N)$

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Technical specifications
Symbols index
External libraries

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 (niebloid)