std::priority_queue(3)

NAME
std::priority_queue - std::priority_queue

Synopsis
   Defined in header <queue>
   template<
   class T,
   class Container = std::vector<T>,
   class Compare = std::less<typename Container::value_type>
   > class priority_queue;
   A priority queue is a container adaptor that provides constant time lookup of the
   largest (by default) element, at the expense of logarithmic insertion and
   extraction.
   A user-provided Compare can be supplied to change the ordering, e.g. using
   std::greater<T> would cause the smallest element to appear as the top().
   Working with a priority_queue is similar to managing a heap in some random access
   container, with the benefit of not being able to accidentally invalidate the heap.

Template parameters
               The type of the stored elements.
   T - The behavior is undefined if T is not the same type as
               Container::value_type.
               (since C++17)
               The type of the underlying container to use to store the elements. The
               container must satisfy the requirements of SequenceContainer, and its
               iterators must satisfy the requirements of LegacyRandomAccessIterator.
               Additionally, it must provide the following functions with the usual
               semantics:
   Container -
                 * front()
                 * push_back()
                 * pop_back()
               The standard containers std::vector and std::deque satisfy these
               requirements.
               A Compare type providing a strict weak ordering.
               Note that the Compare parameter is defined such that it returns true if
   Compare - its first argument comes before its second argument in a weak ordering.
               But because the priority queue outputs largest elements first, the
               elements that "come before" are actually output last. That is, the front
               of the queue contains the "last" element according to the weak ordering
               imposed by Compare.

Member types
   Member type Definition
   container_type Container
   value_compare Compare
   value_type Container::value_type
   size_type Container::size_type
   reference Container::reference
   const_reference Container::const_reference

Member functions
   constructor constructs the priority_queue
                 (public member function)
   destructor destructs the priority_queue
                 (public member function)
   operator= assigns values to the container adaptor
                 (public member function)

Element access
   top accesses the top element
                 (public member function)

Capacity
   empty checks whether the underlying container is empty
                 (public member function)
   size returns the number of elements
                 (public member function)

Modifiers
   push inserts element and sorts the underlying container
                 (public member function)
   emplace constructs element in-place and sorts the underlying container
   (C++11) (public member function)
   pop removes the top element
                 (public member function)
   swap swaps the contents
   (C++11) (public member function)

Member objects
   Container c the underlying container
                 (protected member object)
   Compare comp the comparison function object
                 (protected member object)

Non-member functions
   std::swap(std::priority_queue) specializes the std::swap algorithm
   (C++11) (function template)

Helper classes
   std::uses_allocator<std::priority_queue> specializes the std::uses_allocator type
   (C++11) trait
                        (class template specialization)
  Deduction guides (since C++17)

Example
// Run this code
 #include <functional>
 #include <queue>
 #include <vector>
 #include <iostream>
 template<typename T>
 void print_queue(T q) { // NB: pass by value so the print uses a copy
     while(!q.empty()) {
         std::cout << q.top() << ' ';
         q.pop();
     }
     std::cout << '\n';
 }
 int main() {
     std::priority_queue<int> q;
     const auto data = {1,8,5,6,3,4,0,9,7,2};
     for(int n : data)
         q.push(n);
     print_queue(q);
     std::priority_queue<int, std::vector<int>, std::greater<int>>
         q2(data.begin(), data.end());
     print_queue(q2);
     // Using lambda to compare elements.
     auto cmp = [](int left, int right) { return (left ^ 1) < (right ^ 1); };
     std::priority_queue<int, std::vector<int>, decltype(cmp)> q3(cmp);
     for(int n : data)
         q3.push(n);
     print_queue(q3);
 }

Output:
 9 8 7 6 5 4 3 2 1 0
 0 1 2 3 4 5 6 7 8 9
 8 9 6 7 4 5 2 3 0 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 2684 C++98 priority_queue takes a comparator but lacked added
                       member typedef for it