如何使用构造函数？

Question

我刚刚了解了 C++ 中的类并编写了一个运行良好的代码，但后来我被要求使用构造函数，但我还没有了解它。我今天应该上传这个，如果在课堂上教授这个要求，我会很容易做到这一点，但遗憾的是没有。

在参考了讲义示例后，我尝试根据我所知道的修改代码，但我仍然不确定这个构造函数是如何工作的，或者我应该如何实现它。现在我只尝试将它用于讲师，我将值传递给名为SetLecturerName 的构造函数，但我不确定我还应该做什么。如果有人可以查看此代码并让我知道我哪里出错了，我将不胜感激。

要求是为讲师和课程名称使用构造函数。我想先解决一个，然后单独管理另一个。

    #include <iostream>
    #include <string>   //program uses c++ standard string class


    using namespace std;


    class GradeBook{        //gradebook class definition
    //PUBLIC-------------------------------------------------------------------------------------------------------     
        public:


        //COURSE---------------------------------------------------------------------------------------------------
        void setCourseName(string name){        //function that sets the course name
            courseName = name;      //store the course name in the object
        }

        string getCourseName(){     //function that gets the course name
            return courseName;      //return the object's courseName
        }


        //LECTURER------------------------------------------------------------------------------------------------- 
        /*void setLecturerName(string LecName){     //function that sets the course name
            lecturerName = LecName;     //store the course name in the object
        }*/


        GradeBook(string Lname){
            SetLecturerName(Lname);     //calling the constructor function
        }


        void SetLecturerName(string LecName){       //The constructor function
            lecturerName = LecName;     //store the course name in the object
        }


        string getLecturerName(){       //function that gets the course name
            return lecturerName;        //return the object's courseName
        }   


        //WELCOME MESSAGE------------------------------------------------------------------------------------------ 
        void displayMessage(){      //function that displays a welcome message
            cout << "==================================" << endl;
            cout << "Welcome to the grade book for\n" << getCourseName() << "!" << endl << endl;        //this statement calls getCourseName to get the name of the course this gradebook represents
            cout << "This course is presented by, \n" << getLecturerName() << "." << endl;
            cout << "==================================" << endl;
        }


    //PRIVATE------------------------------------------------------------------------------------------------------
        private:
        string courseName;      //course name for this gradebook
        string lecturerName;        //Lecturer name for this gradebook
    };


    int main(){
        string nameOfCourse;        //string of characters to store the course name
        string nameoflecturer;      //string of characters to store the lecturer name
        GradeBook myGradeBook(nameoflecturer);      //create a GradeBook object named myGradeBook


        //COURSE---------------------------------------------------------------------------------------------------
        cout << "\nPlease enter the course name:" << endl;
        getline(cin, nameOfCourse);     //read a course name with blanks
        myGradeBook.setCourseName(nameOfCourse);        //set the course name


        //LECTURER-------------------------------------------------------------------------------------------------
        cout << "\nPlease enter the Lecturer's name including the title(Ex- Mr.):" << endl;
        getline(cin, nameoflecturer);
        myGradeBook.setLecturerName(nameoflecturer);


        //WELCOME MESSAGE------------------------------------------------------------------------------------------
        cout << endl;
        myGradeBook.displayMessage();       //display message with new course name
    }

Answer 1

就像您现在的代码一样，您首先创建一个带有空讲师的GradeBook 实例，然后在读取讲师时更改讲师。虽然这可行，但首先读取名称然后创建对象会更有意义。

所以你会创建一个类似的构造函数

class GradeBook {
// ...
  GradeBook(string lecturer, string course) {
    lecturerName = lecturer;
    courseName = course;
  }
// ...
}

或者，使用初始化列表：

  GradeBook(string lecturer, string course) :
    lecturerName(lecturer),
    courseName(course)
  { }

在main():

int main() {
    string nameOfCourse;
    string nameoflecturer;

    cout << "\nPlease enter the course name:" << endl;
    getline(cin, nameOfCourse);
    cout << "\nPlease enter the Lecturer's name including the title(Ex- Mr.):" << endl;
    getline(cin, nameoflecturer);

    GradeBook myGradeBook(nameoflecturer, nameOfCourse);
    // ...
}