std::make_heap

default (1)	template <class RandomAccessIterator> void make_heap (RandomAccessIterator first, RandomAccessIterator last);
custom (2)	template <class RandomAccessIterator, class Compare> void make_heap (RandomAccessIterator first, RandomAccessIterator last, Compare comp );

default (1)

template <class RandomAccessIterator>  void make_heap (RandomAccessIterator first, RandomAccessIterator last);

custom (2)

template <class RandomAccessIterator, class Compare>  void make_heap (RandomAccessIterator first, RandomAccessIterator last,                  Compare comp );

Make heap from range

Rearranges the elements in the range [first,last) in such a way that they form a heap.

A heap is a way to organize the elements of a range that allows for fast retrieval of the element with the highest value at any moment (with pop_heap), even repeatedly, while allowing for fast insertion of new elements (with push_heap).

The element with the highest value is always pointed by first. The order of the other elements depends on the particular implementation, but it is consistent throughout all heap-related functions of this header.

The elements are compared using operator< (for the first version), or comp (for the second): The element with the highest value is an element for which this would return false when compared to every other element in the range.

The standard container adaptor priority_queue calls make_heap, push_heap and pop_heap automatically to maintain heap properties for a container.

Parameters

first, last: Random-access iterators to the initial and final positions of the sequence to be transformed into a heap. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
RandomAccessIterator shall point to a type for which swap is properly defined and which is both move-constructible and move-assignable.
comp: Binary function that accepts two elements in the range as arguments, and returns a value convertible to bool. The value returned indicates whether the element passed as first argument is considered to be less than the second in the specific strict weak ordering it defines.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.

Return value

none

Example

// range heap example
#include <iostream>     // std::cout
#include <algorithm>    // std::make_heap, std::pop_heap, std::push_heap, std::sort_heap
#include <vector>       // std::vector

int main () {
  int myints[] = {10,20,30,5,15};
  std::vector<int> v(myints,myints+5);

  std::make_heap (v.begin(),v.end());
  std::cout << "initial max heap   : " << v.front() << '\n';

  std::pop_heap (v.begin(),v.end()); v.pop_back();
  std::cout << "max heap after pop : " << v.front() << '\n';

  v.push_back(99); std::push_heap (v.begin(),v.end());
  std::cout << "max heap after push: " << v.front() << '\n';

  std::sort_heap (v.begin(),v.end());

  std::cout << "final sorted range :";
  for (unsigned i=0; i<v.size(); i++)
    std::cout << ' ' << v[i];

  std::cout << '\n';

  return 0;
}

Output:

initial max heap   : 30
max heap after pop : 20
max heap after push: 99
final sorted range : 5 10 15 20 99

Complexity

Up to linear in three times the distance between first and last: Compares elements and potentially swaps (or moves) them until rearranged as a heap.

Data races

The objects in the range [first,last) are modified.

Exceptions

Throws if any of the element comparisons, the element swaps (or moves) or the operations on iterators throws.
Note that invalid arguments cause undefined behavior.