How to use the priority queue STL for objects?

by

You need to provide a valid strict weak ordering comparison for the type stored in the queue, Person in this case. The default is to use std::less<T>, which resolves to something equivalent to operator<. This relies on it’s own stored type having one. So if you were to implement

bool operator<(const Person& lhs, const Person& rhs);

it should work without any further changes. The implementation could be

bool operator<(const Person& lhs, const Person& rhs)
{
  return lhs.age < rhs.age;
}

If the the type does not have a natural “less than” comparison, it would make more sense to provide your own predicate, instead of the default std::less<Person>. For example,

struct LessThanByAge
{
  bool operator()(const Person& lhs, const Person& rhs) const
  {
    return lhs.age < rhs.age;
  }
};

then instantiate the queue like this:

std::priority_queue<Person, std::vector<Person>, LessThanByAge> pq;

Concerning the use of std::greater<Person> as comparator, this would use the equivalent of operator> and have the effect of creating a queue with the priority inverted WRT the default case. It would require the presence of an operator> that can operate on two Person instances.

More Related Contents:

  1. In which scenario do I use a particular STL container?
  2. C++ sorting and keeping track of indexes
  3. What are the complexity guarantees of the standard containers?
  4. Remove spaces from std::string in C++
  5. problem sorting using member function as comparator
  6. How to initialize std::vector from C-style array?
  7. string c_str() vs. data()
  8. std::transform() and toupper(), no matching function
  9. Case insensitive std::string.find()
  10. Does std::list::remove method call destructor of each removed element?
  11. What is the difference between const_iterator and non-const iterator in the C++ STL?
  12. Should I store entire objects, or pointers to objects in containers?
  13. I want to convert std::string into a const wchar_t *
  14. what is the best modern c++ approach to construct and manipulate a 2d array [closed]
  15. How do you copy the contents of an array to a std::vector in C++ without looping?
  16. How to read and write a STL C++ string?
  17. What is the meaning of numeric_limits::digits10
  18. How to check that an element is in a std::set?
  19. Determine if map contains a value for a key?
  20. Why would I prefer using vector to deque
  21. What the heque is going on with the memory overhead of std::deque?
  22. How to remove constness of const_iterator?
  23. std::vector removing elements which fulfill some conditions
  24. How can std::make_heap be implemented while making at most 3N comparisons?
  25. What is the right approach when using STL container for median calculation?
  26. Is there support in C++/STL for sorting objects by attribute?
  27. Converting between C++ std::vector and C array without copying
  28. C++, can I statically initialize a std::map at compile time?
  29. what does `using std::swap` inside the body of a class method implementation mean?
  30. STL algorithms: Why no additional interface for containers (additional to iterator pairs)?

Leave a Comment