c++使用初始化列表来初始化字段

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#include<iostream> using namespace std;   class Student1 { private:     int _a;     int _b;   public:     void     fprint()     {         cout << " a = " << _a << " " << "b = " << _b << endl;     }       //Student1(int i):b(i),a(b){ }    //异常顺序：发现a的值为0  b的值为2  说明初始化仅仅对b有效果，对a没有起到初始化作用           Student1(int a, int b): _a(a), _b(b)     {         cout << "constructor" << endl;     } //正常顺序：发现a = b = 2 说明两个变量都是初始化了的       Student1()                         // 无参构造函数     {         cout << "默认构造函数Student1" << endl ;     }       Student1(const Student1 &t1) //拷贝构造函数     {         cout << "拷贝构造函数Student1" << endl ;         this->_a = t1._a;         this->_b = t1._b;     }       Student1 &     operator = (const Student1 &t1) // 赋值运算符     {         cout << "赋值函数Student1" << endl ;         this->_a = t1._a ;         this->_b = t1._b ;         return *this;     }   };   class Teacher { public:     Student1 test;  //类中包含类     Teacher(Student1 &t1)     {         test  = t1 ;     } };   int main(void) {     Student1 A(2,4);      //进入默认构造函数     Teacher B(A);        //进入拷贝构造函数     A.fprint();           //输出前面初始化的结果     B.test.fprint(); }