Struct ordering criteria of a priority queue in C++

Question

I was wondering if it is possible to order two different priority_queues (stl) with the same struct but with a different ordering criteria. Imagine something like:

struct stuff {
  int a, b;
}

priority_queue<stuff> a;
priority_queue<stuff> b;

Note that this is not functional code of C++, just pseudocode. Then, I would like to know if it is possible that a and b differ in the ordering, one with the biggest stuff.a at the start of the queue and the other one with the biggest stuff.b.

Thank you very much!

Marc

Answer 1

Documentation on std::priority_queue has an example how to use lambda with it, so just create 2 of them:

struct stuff {
  int a, b;
};

void foo() 
{
    auto cmpBiggerA = []( const stuff &s1, const stuff &s2 ) { return s1.a > s2.a; };
    auto cmpBiggerB = []( const stuff &s1, const stuff &s2 ) { return s1.b > s2.b; };

    priority_queue<stuff,std::vector<stuff>,decltype(cmpBiggerA)> a( cmpBiggerA );
    priority_queue<stuff,std::vector<stuff>,decltype(cmpBiggerB)> b( cmpBiggerB );
}