Template function for increasing and decreasing priority queue - c++

Question

I wanted to write a template function for printing increasing and decreasing priority queues. Currently I have implemented it as
void print_queue1(priority_queue<int> q, string s){
cout << "Value of prior queue " << s << " is : [";
while(!q.empty()){
cout << " " << q.top() << ",";
q.pop();
}
cout << "]" << endl;
}
// min-heap
void print_queue2(priority_queue<int, vector<int>, greater<int>> q, string s){
cout << "Value of prior queue " << s << " is : [";
while(!q.empty()){
cout << " " << q.top() << ",";
q.pop();
}
cout << "]" << endl;
}
Is there some way to write a single template function that can do this?

Answer 1

You can use a variadic function template for this. Since the logic is the same regardless of the queue type, we can just accept any type of queue like
template <typename... Params>
void print_queue(priority_queue<Params...> q, string s){
cout << "Value of prior queue " << s << " is : [";
while(!q.empty()){
cout << " " << q.top() << ",";
q.pop();
}
cout << "]" << endl;
}
Here, Params will be deduced from the template parameters of the supplied priority_queue for you by the compiler and it will stamp out a concrete function for each different parameter set.

Answer 2

The template class std::priority_queue uses three template type parameters.
template<
class T,
class Container = std::vector<T>,
class Compare = std::less<typename Container::value_type>
> class priority_queue;
You may use those same three parameters in your function to accept any instantiation of std::priority_queue.
template<class T, class Container, class Compare>
void print_queue(priority_queue<T,Container,Compare> q, string s){
cout << "Value of prior queue " << s << " is : [";
while(!q.empty()){
cout << " " << q.top() << ",";
q.pop();
}
cout << "]" << endl;
}
Or, you may remove/restrict any one of them to enforce a subset of priority queues..
template<class Container, class Compare>
void print_queue(priority_queue<int,Container,Compare> q, string s){
// This function is really only designed for priority queues of int!
cout << "Value of prior queue " << s << " is : [";
while(!q.empty()){
cout << " " << q.top() << ",";
q.pop();
}
cout << "]" << endl;
}