对类成员进行排序时得到错误未解决的重载函数类型

Question

class S {
    public:
        vector <int> ia;
        int rank;
        bool cmp(S const &s1, S const &s2) {
            return (s1.rank > s2.rank);
        }
        void sort_on_rank() {
            sort(ia.begin(), ia.end(), cmp);
        }
};

This piece of code is trying to sort the vector on rank, but doesn't compile because of following error,
[Error] no matching function for call to 'sort(std::vector::iterator, std::vector::iterator, )'

Please help me on this and tell where is the problem.

Answer 1

From your program it seems you want to sort objects of S classes. In that case your vector should be like this : std::vector<S> .

Your cmp is a non-static member function of class S and hence std::sort cannot work with it. (Think about how will you use the function).

You can either overload < operator for your class or pass a stand-alone/static member function or you can use C++11 lambda expression.

Thus your class becomes:

class S {
    public:
        vector<S> ia;
        int rank;
        void sort_on_rank() {
            sort(ia.begin(), ia.end(), 
                 [] (S const &s1, S const &s2) {
                     return (s1.rank > s2.rank);
                 });
        }
};

However if you want to merely sort vector containing int in descending order, just call std::sort with a C++11 lambda that returns lhs > rhs .

std::sort(ia.begin(), ia.end(), [](int x, int y) { return x > y; });

Answer 2

您的S::cmp()接受S ，但S::ia的值类型为int 。