• [first, last) is a valid range.
• [first, last – 1) is a valid range. That is, [first, last) is nonempty.
• [first, last – 1) is a heap. That is, is_heap(first, last – 1) is true.
For the second version:
• [first, last) is a valid range.
• [first, last – 1) is a valid range. That is, [first, last) is nonempty.
• [first, last) is a heap. That is, is_heap(first, last – 1, comp) is true.
Complexity Logarithmic. At most 2 * log(last – first) comparisons.
Example int main() {
int A[] = {1, 2, 3, 4, 5, 6};
const int N = sizeof(A) / sizeof(int);
make_heap(A, A+N);
cout << 'Before pop: ';
copy(A, A+N, ostream_iterator<int>(cout, ' '));
pop_heap(A, A+N);
cout << endl << 'After pop: ';
copy(A, A+N-1, ostream_iterator<int>(cout, ' '));
cout << endl << 'A[N-1] = ' << A[N-1] << endl;
}
The output is
Before pop: 6 5 3 4 2 1
After pop: 5 4 3 1 2
A[N-1] = 6
Notes [1] A heap is a particular way of ordering the elements in a range of Random Access Iterators [f, l). The reason heaps are useful (especially for sorting, or as priority queues) is that they satisfy two important properties. First, *f is the largest element in the heap. Second, it is possible to add an element to a heap (using push_heap), or to remove *f, in logarithmic time. Internally, a heap is a tree represented as a sequential range. The tree is constructed so that that each node is less than or equal to its parent node.
[2] Pop_heap removes the largest element from a heap, and shrinks the heap. This means that if you call keep calling pop_heap until only a single element is left in the heap, you will end up with a sorted range where the heap used to be. This, in fact, is exactly how sort_heap is implemented.
See also make_heap, push_heap, sort_heap, is_heap, sort
Category: algorithms
Component type: function
Prototype Make_heap is an overloaded name; there are actually two make_heap functions.
template <class RandomAccessIterator>
void make_heap(RandomAccessIterator first, RandomAccessIterator last);
template <class RandomAccessIterator, class StrictWeakOrdering>
void make_heap(RandomAccessIterator first, RandomAccessIterator last, StrictWeakOrdering comp);
Description Make_heap turns the range [first, last) into a heap [1].
The two versions of make_heap differ in how they define whether one element is less than another. The first version compares objects using operator<, and the second compares objects using a function object comp. In the first version the postcondition is that is_heap(first, last) is true, and in the second version the postcondition is that is_heap(first, last, comp) is true.
Definition Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.
Requirements on types For the first version:
• RandomAccessIterator is a model of Random Access Iterator.
• RandomAccessIterator is mutable.
• RandomAccessIterator's value type is a model of LessThan Comparable.
• The ordering on objects of RandomAccessIterator's value type is a strict weak ordering, as defined in the LessThan Comparable requirements.
For the second version:
• RandomAccessIterator is a model of Random Access Iterator.
• RandomAccessIterator is mutable.
• StrictWeakOrdering is a model of Strict Weak Ordering.
• RandomAccessIterator's value type is convertible to StrictWeakOrdering's argument type.
Preconditions • [first, last) is a valid range.
Complexity Linear. At most 3*(last – first) comparisons.
Example int main() {
int A[] = {1, 4, 2, 8, 5, 7};
const int N = sizeof(A) / sizeof(int);
make_heap(A, A+N);
copy(A, A+N, ostream_iterator<int>(cout, ' '));
cout << endl;
sort_heap (A, A+N);
copy(A, A+N, ostream_iterator <int>(cout, ' '));
cout << endl;
}
Notes 
