stl priority_queue of C++ with struct

Question

How can we use STL priority_queue for struct ? Any illustration of pushing & popping , where struct has multiple data-types?
Say : struct thing { int a; char b;} glass[10]; .
Now how can i put this struct on priority_queue using 'int a' for ordering ?

Answer 1

Here is a slightly modified answer to your original question, which you deleted for no apparent reason. The original contained enough information for you to figure this out, but here it goes: provide a less than comparison that uses the int for comparison.

All you need to do is provide a functor that implements a less-than comparison with strict weak ordering, or a less-than operator for your class implementing the same. This struct satisfies the requirements:

struct thing
{
    int a;
    char b;
    bool operator<(const thing& rhs) const
    {
        return a < rhs.a;
    }
};

then

std::priority_queue<thing> q;
thing stuff = {42, 'x'};
q.push(stuff);
q.push(thing{4242, 'y'}); // C++11 only
q.emplace(424242, 'z'); // C++11 only    
thing otherStuff = q.top();
q.pop();

Answer 2

Overload < operator for thing :

struct thing
{
    int a;
    char b;

    bool operator<(const thing &o) const
    {
        return a < o.a;
    }
};

priority_queue<thing> pq;

thing t1, t2, t3;

// ...

pq.push(t1);
pq.push(t2);

// ...

t3 = pq.top();
pq.pop();

Answer 3

You need to implement a compare function or overload operator to tell priority queue that on which order you want to sort your custom data. When priority queue will sort your data then it will need a way to know how to compare among them. You have to specify this by passing a function to priority queue or overloading operator in you custom data class or structure.

You can check this answer. This might help you. I have tried to explain multiple ways of using priority queue for custom data types.