C++ 仿函数使用讲解

 
//统计长度小于5的string的个数
 bool LengthIsLessThanFive(const string& str) {
      return str.length()<5;    
 }

int main()
 {	
         vector<string> vec = { "asdd","asddsa","dssa","asd" };
	 int res1 = count_if(vec.begin(), vec.end(), LengthIsLessThanFive);
}

//统计长度小于len的string的个数
 bool LengthIsLessThanFive(const string& str, int len) {
      return str.length()< len;
 }

 int maxLength=5;
 
 //统计长度小于len的string的个数
 bool LenthIsLessThanCustom(const string& str) {
	     return str.length() < maxLength;
	 
 }

class Func {
public:
   void operator() (const string& str) const {
	cout << str << endl;
   }
 
};

int main()
{
    Func myFunc;
    myFunc("helloworld!");
}

 
struct ShorterThan {
 public:
	 explicit ShorterThan(int maxLength) : length(maxLength) {}
	 bool operator() (const string& str) const {
		 return str.length() < length;
 
	 }
 private:
	 const int length;
 
 };
;
 
 int main()
 {
	
 
	 vector<string> vec = { "asdd","asddsa","dssa","asd" };
	 int res3 = count_if(vec.begin(), vec.end(), ShorterThan(5));
	 cout << res3 << endl;
}

 template<typename T> struct comp
 {
	 bool operator()(T in1, T in2) const
	 {
		 return (in1 > in2);
	 }
 };
 
 
 int main()
 {
    comp<int> m_comp_objext;
    cout << m_comp_objext(6, 3) << endl;     //一、使用对象调用
    cout << comp<int>()(6, 3) << endl;       //二、使用临时对象
    return 0;
}