C++——仿函数

class StringAppend{
    public:
        explicit StringAppend(const string& str) : ss(str){}

        void operator() (const string& str) const{
             cout<<str<<‘ ‘<<ss<<endl;
        }
    
    private:
        const string ss;  
};

StringAppend myFunc("is world");
myFunc("hello");
>>>hellois world

class ShorterThan {
    public:
        explicit ShorterThan(int maxLength) : length(maxLength) {}
        bool operator() (const string& str) const {
            return str.length() < length;
        }
    private:
        const int length;
};

count_if(myVector.begin(), myVector.end(), ShorterThan(length));//直接调用即可