std::pop_heap

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

Swaps the value in the position first and the value in the position last-1 and makes the subrange [first, last-1) into a max heap. This has the effect of removing the first (largest) element from the heap defined by the range [first, last).

The first version of the function uses operator< to compare the elements, the second uses the given comparison function comp.

Parameters

first, last	-	the range of elements defining the valid nonempty heap to modify
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); The signature does not need to have const &, but the function object must not modify the objects passed to it. 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 RandomAccessIterator.
- The type of dereferenced `RandomIt` must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

At most 2log(N) comparisons where N=std::distance(first, last).

Notes

A max heap is a range of elements [f,l) that has the following properties:

With N = l - f, for all 0 < i < N, f[floor(i-1 2)] does not compare less than f[i].
a new element can be added using std::push_heap()
the first element can be removed using std::pop_heap()

Example

Run this code

#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());

    std::cout << "v: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';

    std::pop_heap(v.begin(), v.end()); // moves the largest to the end

    std::cout << "after pop_heap: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';

    int largest = v.back();
    v.pop_back();  // actually removes the largest element
    std::cout << "largest element: " << largest << '\n';

    std::cout << "heap without largest: ";
    for (auto i : v) std::cout << i << ' ';
    std::cout << '\n';
}

Output:

v: 9 5 4 1 1 3 
after pop_heap: 5 3 4 1 1 9 
largest element: 9
heap without largest: 5 3 4 1 1

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications