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;
   The 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
   T - The type of the stored elements. The program is ill-formed if T is not
               the same type as Container::value_type.
               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(), e.g., std::vector::front(),
                 * push_back(), e.g., std::deque::push_back(),
                 * pop_back(), e.g., std::vector::pop_back().
               The standard containers std::vector (including std::vector<bool>) 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 objects
   Member name Definition
   Container c the underlying container
                (protected member object)
   Compare comp the comparison function object
                (protected member object)

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 container adaptor 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)
   push_range inserts a range of elements and sorts the underlying container
   (C++23) (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)

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)
   std::formatter<std::priority_queue> formatting support for std::priority_queue
   (C++23) (class template specialization)
     Deduction guides (since C++17)

Notes
       Feature-test macro Value Std Feature
   __cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion
                        for containers

Example
// Run this code
 #include <functional>
 #include <iostream>
 #include <queue>
 #include <string_view>
 #include <vector>
 template<typename T>
 void pop_println(std::string_view rem, T& pq)
 {
     std::cout << rem << ": ";
     for (; !pq.empty(); pq.pop())
         std::cout << pq.top() << ' ';
     std::cout << '\n';
 }
 template<typename T>
 void println(std::string_view rem, const T& v)
 {
     std::cout << rem << ": ";
     for (const auto& e : v)
         std::cout << e << ' ';
     std::cout << '\n';
 }
 int main()
 {
     const auto data = {1, 8, 5, 6, 3, 4, 0, 9, 7, 2};
     println("data", data);
     std::priority_queue<int> max_priority_queue;
     // Fill the priority queue.
     for (int n : data)
         max_priority_queue.push(n);
     pop_println("max_priority_queue", max_priority_queue);
     // std::greater<int> makes the max priority queue act as a min priority queue.
     std::priority_queue<int, std::vector<int>, std::greater<int>>
         min_priority_queue1(data.begin(), data.end());
     pop_println("min_priority_queue1", min_priority_queue1);
     // Second way to define a min priority queue.
     std::priority_queue min_priority_queue2(data.begin(), data.end(), std::greater<int>());
     pop_println("min_priority_queue2", min_priority_queue2);
     // Using a custom function object to compare elements.
     struct
     {
         bool operator()(const int l, const int r) const { return l > r; }
     } customLess;
     std::priority_queue custom_priority_queue(data.begin(), data.end(), customLess);
     pop_println("custom_priority_queue", custom_priority_queue);
     // 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)> lambda_priority_queue(cmp);
     for (int n : data)
         lambda_priority_queue.push(n);
     pop_println("lambda_priority_queue", lambda_priority_queue);
 }

Output:
 data: 1 8 5 6 3 4 0 9 7 2
 max_priority_queue: 9 8 7 6 5 4 3 2 1 0
 min_priority_queue1: 0 1 2 3 4 5 6 7 8 9
 min_priority_queue2: 0 1 2 3 4 5 6 7 8 9
 custom_priority_queue: 0 1 2 3 4 5 6 7 8 9
 lambda_priority_queue: 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 307 C++98 Container could not be allowed
                       std::vector<bool>
   LWG 2566 C++98 Missing the requirement for ill-formed if T is not the same
                       Container::value_type type as Container::value_type
                       priority_queue takes a
   LWG 2684 C++98 comparator added
                       but lacked member typedef for
                       it

See also
   vector dynamic contiguous array
                (class template)
   vector<bool> space-efficient dynamic bitset
                (class template specialization)
   deque double-ended queue
                (class template)