| 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
| T | - | The type of the stored elements. |
| Container | - | 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 RandomAccessIterator. Additionally, it must provide the following functions with the usual semantics:
The standard containers |
| Compare | - | A Compare type providing a strict weak ordering. |
Member types
| Member type | Definition |
|---|---|
container_type | Container |
value_type | Container::value_type |
size_type | Container::size_type |
reference | Container::reference |
const_reference | Container::const_reference |
Member functions
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 | |
| accesses the top element (public member function) | |
Capacity | |
| checks whether the underlying container is empty (public member function) | |
| returns the number of elements (public member function) | |
Modifiers | |
| inserts element and sorts the underlying container (public member function) | |
| (C++11) | constructs element in-place and sorts the underlying container (public member function) |
| removes the top element (public member function) | |
| swaps the contents (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
specializes the std::swap algorithm (function template) |
Helper classes
specializes the std::uses_allocator type trait (function template) |
Example
#include <functional>
#include <queue>
#include <vector>
#include <iostream>
template<typename T> void print_queue(T& q) {
while(!q.empty()) {
std::cout << q.top() << " ";
q.pop();
}
std::cout << '\n';
}
int main() {
std::priority_queue<int> q;
for(int n : {1,8,5,6,3,4,0,9,7,2})
q.push(n);
print_queue(q);
std::priority_queue<int, std::vector<int>, std::greater<int> > q2;
for(int n : {1,8,5,6,3,4,0,9,7,2})
q2.push(n);
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 : {1,8,5,6,3,4,0,9,7,2})
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
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