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std::priority_queue(3) C++ Standard Libary 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 inser- tion 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 inval- idate 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 SequenceCon- tainer, and its iterators must satisfy the requirements of LegacyRando- mAccessIterator. 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::vec- tor<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 specializa- tion) std::formatter<std::priority_queue> formatting support for std::priority_queue (C++23) (class template specializa- tion) Deduction guides (since C++17) Notes Feature-test macro Value Std Feature __cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construc- tion 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 retroac- tively 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 Con- tainer::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) http://cppreference.com 2024.06.10 std::priority_queue(3)
NAME | Synopsis | Template parameters | Member types | Member objects | Member functions | Element access | Capacity | Modifiers | Non-member functions | Helper classes | Notes | Example | Output: | See also
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