CODEWITHSUNDEEP
c++data-structuresstlcontainerspriority-queue
Saeid
Saeid

Reputation: 4265

What's the use of passing a container to priority_queue

Every time you want to use a custom compare function for a priority_queue you have to pass it a container too. It seems to me, you should always pass a vector<T> to it. Now at first I thought this is some kind of redundancy, but it shouldn't be the case. What's the use of passing a container to a priority_queue and how can I make use of it?

Upvotes: 2

Views: 1269

Answers (2)

Nick Cano
Nick Cano

Reputation: 457

You're simply passing it the underlying container type which, by default, is std::vector<T>. If you want to retain the default behavior then you're correct in saying you can always pass std::vector<T>. You can also use std::deque<T>, or any custom container that exposes the following functions:

  • empty()
  • size()
  • front()
  • push_back()
  • pop_back()

But why must you specify a container before you can specify a comparator? Well, it just has to do with how the parameters are defined. container and compare are both default parameters, and container just happens to come first. Because of the way C++ works, you just have to pass all the parameters leading up to compare before you can pass it, meaning you have to also pass container. AFAIK it has nothing to do with compare needing to know anything about container.

Upvotes: 3

Brian Bi
Brian Bi

Reputation: 119219

std::priority_queue is a container adaptor. It doesn't actually know how to store the elements you put in it; it delegates that to a real container such as std::vector. It's rare that you'll want to use something other than std::vector as the underlying container, but you could use std::deque if you want to.

std::vector is the default, but since this is the second template argument, if you want to use a non-default value for the third template argument, you're forced to specify the second one, just like with function arguments.

Upvotes: 6

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