std::priority_queue<T,Container,Compare>::top

 

C++

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Feature test macros (C++20)

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Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

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set

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multimap

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unordered_set (C++11)

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unordered_map (C++11)

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Adaptors

stack

queue

priority_queue

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span (C++20)

 

std::priority_queue

Member functions

priority_queue::priority_queue

priority_queue::~priority_queue

priority_queue::operator=

Element access

priority_queue::top

Capacity

priority_queue::empty

priority_queue::size

Modifiers

priority_queue::push

priority_queue::emplace (C++11)

priority_queue::pop

priority_queue::swap (C++11)

Non-member functions

std::swap (C++11)

Deduction guides(C++17)

 

const_reference top() const;

Returns reference to the top element in the priority queue. This element will be removed on a call to pop(). If default comparison function is used, the returned element is also the greatest among the elements in the queue.

Parameters

(none)

Return value

Reference to the top element as if obtained by a call to c.front()

Complexity

Constant.

Example

Run this code

#include <queue>
#include <iostream>
 
struct Event
{
    int priority{};
    char data{' '};
 
    friend bool operator< (Event const& lhs, Event const& rhs) {
        return lhs.priority < rhs.priority;
    }
 
    friend std::ostream& operator<< (std::ostream& os, Event const& e) {
        return os << "{ " << e.priority << ", '" << e.data << "' } ";
    }
};
 
int main()
{
    std::priority_queue<Event> events;
 
    std::cout << "Fill the events queue:\n";
 
    for (auto const e: { Event{6,'L'}, {8,'I'}, {9,'S'}, {1,'T'}, {5,'E'}, {3,'N'} }) {
        std::cout << e << ' ';
        events.push(e);
    }
 
    std::cout << "\n" "Process events:\n";
 
    for (; !events.empty(); events.pop()) {
        Event const& e = events.top();
        std::cout << e << ' ';
    }
}

Output:

Fill the events queue:
{ 6, 'L' }  { 8, 'I' }  { 9, 'S' }  { 1, 'T' }  { 5, 'E' }  { 3, 'N' }
Process events:
{ 9, 'S' }  { 8, 'I' }  { 6, 'L' }  { 5, 'E' }  { 3, 'N' }  { 1, 'T' }

See also

pop	removes the top element (public member function)