std::pop_heap - cppreference.com
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    std::pop_heap

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    C++
     
    Algorithm library
    Constrained algorithms and algorithms on ranges (C++20)
    Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
    Non-modifying sequence operations    
    Batch operations
    (C++17)
    Search operations
    Modifying sequence operations
    Copy operations
    (C++11)
    (C++11)
    (C++11)
    Swap operations
    Transformation operations
    Generation operations
    Removing operations
    Order-changing operations
    (until C++17)(C++11)
    (C++20)(C++20)
    Sampling operations
    (C++17)

    Sorting and related operations
    Partitioning operations
    (C++11)    
    (C++11)

    Sorting operations
    Binary search operations
    (on partitioned ranges)
    Set operations (on sorted ranges)
    Merge operations (on sorted ranges)
    Heap operations
    Minimum/maximum operations
    (C++11)
    (C++17)
    Lexicographical comparison operations
    (C++20)
    Permutation operations


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

    Removes the first element from the non-empty heap represented by the target range [first, last) by swapping the value at first and the value at last - 1. The heap after the removal will be [first, last - 1).

    1) The heap is with respect to operator<(until C++20)std::less{}(since C++20).
    If [first, last) is not a valid non-empty heap with respect to operator<(until C++20)std::less{}(since C++20), the behavior is undefined.
    2) The heap is with respect to comp.
    If [first, last) is not a valid non-empty heap with respect to comp, the behavior is undefined.

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

    (until C++11)
    (since C++11)

    Parameters

    first, last - the pair of iterators defining the target range
    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 N as std::distance(first, last):

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

    Example

    Run this code
    #include <algorithm>
#include <iostream>
#include <string_view>
#include <type_traits>
#include <vector>
 
void println(std::string_view rem, const auto& v)
{
    std::cout << rem;
    if constexpr (std::is_scalar_v<std::decay_t<decltype(v)>>)
        std::cout << v;
    else
        for (int e : v)
            std::cout << e << ' ';
    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);
    
    std::pop_heap(v.begin(), v.end()); // moves the largest to the end
    println("after pop_heap:  ", v);
    
    int largest = v.back();
    println("largest element: ", largest);
    
    v.pop_back(); // actually removes the largest element
    println("after pop_back:  ", v);
}

    Output: 

    after make_heap: 9 5 4 1 1 3
after pop_heap:  5 3 4 1 1 9
largest element: 9
after pop_back:  5 3 4 1 1

    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 1205 C++98 the behavior was unclear if the target range is empty the behavior is undefined in this case

    See also