Find and access the element in a Priority Queue in C++11

Question

How to find an element in a priority queue of C++11 and access the respective element? As for the following example: What would be the best to check the existence of an element in the priority queue Q and access it. Is it also possible to edit it ?

Intention: Writing an application, in which I have to check whether a particular object has been inserted into priority queue or not. If it is being inserted, then I need to access that particular object and possibly update it.

#include <iostream>
#include <vector>
#include <string>
#include <queue>

struct Person {
    int val;
    std::string y;
    bool operator()(const Person& lhs, const Person& rhs) const
  {
    return lhs.val > rhs.val;
  }
    };

int main () {

    std::vector<int> data = {5,4,3,2,1};
    Person X1,X2,X3,X4,X5;
    X1.val = 20;
    X1.y = "twenty";

    X2.val = 10;
    X2.y = "ten";

    X3.val = 50;
    X3.y = "fifty";

    X4.val = 5;
    X4.y = "five";

    X5.val = 0;
    X5.y = "zero";

    std::vector<Person> V; 
    V.push_back(X1);
    V.push_back(X2);
    V.push_back(X3);
    V.push_back(X4);
    V.push_back(X5);

    std::priority_queue<Person,std::vector<Person>,Person> Q; 

    for (auto x: V) Q.push(x);
    return 0;
}

Answer 1

For this usage, I'd suggest you use a combination of std::priority_queue and an std::unordered_map.

Let's restructure your data as follows:

struct PersonInfo {
    std::string y;
};

This contains the mutable information about a person.

Now you have two containers:

• an std::priority_queue<int> of the values which were previously the vals in your Person class objects.

• an std::unordered_map<int, PersonInfo> mapping these values into PersonInfos.

For your stated intent

in which I have to check whether a particular object has been inserted into priority queue or not.

Simply check if things were inserted using the map; make sure to update it when pushing and popping the priority queue, though.

If it is being inserted, then I need to access that particular object and possibly update it.

Just use the unordered map.