std::pop_heap

 

C++

Compiler support

Freestanding and hosted

Language

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

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)	execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)(C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	search search_n lexicographical_compare lexicographical_compare_three_way (C++20)	findfind_iffind_if_not (C++11) find_end find_first_of
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)
C library
qsort	bsearch

 

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 heap. This has the effect of removing the first element from the heap defined by the range [first, last).

The first version of the function uses operator< to compare the elements, which makes the heap a max heap. 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); 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.

Return value

(none)

Complexity

At most 2×log(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[(i-1)/2] does not compare less than f[i].
• A new element can be added using std::push_heap, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time.
• The first element can be removed using std::pop_heap, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time.

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

See also

push_heap	adds an element to a max heap (function template)
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)
sort_heap	turns a max heap into a range of elements sorted in ascending order (function template)
ranges::pop_heap (C++20)	removes the largest element from a max heap (niebloid)