priority_queue

This is a discussion on priority_queue within the C++ Programming forums, part of the General Programming Boards category; I'm looking to create a priority_queue with the vector created in main() using B::weight to order the queue. How might ...

  1. #1
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    priority_queue

    I'm looking to create a priority_queue with the vector created in main() using B::weight to order the queue. How might I go about doing that?

    Code:
    #include <vector>
    #include <string>
    
    template <typename T>
    class A
    {
    public:
    	class B
    	{
    	private:
    		B()
    		{
    			weight = 0;
    		}
    		T data;
    		int weight;
    		friend class A;
    	public:
    		int get_weight()
    		{
    			return weight;
    		}
    		
    		bool operator==(const B& rhs) const
    		{
    			return (*this).weight == rhs.weight;
    		}
    
    		bool operator<(const B& rhs) const
    		{
    			return (*this).weight < rhs.weight;
    		}
    
    		bool operator>(const B& rhs) const
    		{
    			return (*this).weight > rhs.weight;
    		}
    	};
    	A() {}
    	virtual ~A() {}
    	B* create_B(T data, int weight = 0);
    };
    
    template <typename T>
    typename A<T>::B* A<T>::create_B(T data, int weight = 0)
    {
    	B* new_B = new B;
    	new_B->data = data;
    	new_B->weight = weight;
    	return new_B;
    }
    
    int main()
    {
    	A<std::string> myA;
    	std::vector<A<std::string>::B*> stuff;
    	stuff.push_back(myA.create_B("string1", 1));
    	stuff.push_back(myA.create_B("string2", 2));
    
    	return 0;
    }

  2. #2
    C++ Witch laserlight's Avatar
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    It looks like operator< is already correctly defined so you can #include <queue> and use a std::priority_queue<A<std::string>::B>.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    That works great, but I need the queue to hold type B*, not B, so:
    Code:
    std::priority_queue<A<std::string>::B*>
    The problem is, I still need it to sort using operator< (or B::weight). How would I go about doing such a thing?

  4. #4
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    make a wrapper class perhaps?

  5. #5
    and the Hat of Guessing tabstop's Avatar
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    Or write a custom sort function object that sorts objects of type B* by referring to the objects to which they point.

  6. #6
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    Quote Originally Posted by tabstop View Post
    Or write a custom sort function object that sorts objects of type B* by referring to the objects to which they point.
    I'm assuming, then, that I couldn't convince std::sort() to do the job on a vector of B*?

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    Of course, you can. But remember what sort looks like:
    Code:
    void sort ( RandomAccessIterator first, RandomAccessIterator last, Compare comp );
    You need to tell sort when things are less than other things.

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