学生用书程序 - 需要在其中插入复制构造函数

如何解决学生用书程序 - 需要在其中插入复制构造函数

我需要编写一个程序，定义一个存储姓名信息的学生类CStudent， 学生的教号和专业提供： 使用复制构造函数创建对象 使用显式构造函数（带参数）创建对象

问题是，我不知道从哪里进入构造函数。这是我到达的代码以及我如何编写它。

#include <iostream>



using namespace std;
#define max 10
 class CStudent
{
private:
    char name[30];
    int facnum;
    char specialty[20];

public:
    void getDetails(void);
    void putDetails(void);
};

void CStudent::getDetails(void) {
    cout << "enter name: ";
    cin >> name;
    cout << "enter facnum:";
    cin >> facnum;
    cout << "Enter student speacialty: ";
    cin >> specialty;

}

void CStudent::putDetails(void) {

    cout << " Student details: \n";
    cout << " Name:" << name << ",facnum: " << facnum << ",Specialty: " << specialty;

}

int main()
{
    CStudent std[max];     
    int n,loop;

    cout << "Enter total number of students: ";
    cin >> n;

    for (loop = 0; loop < n; loop++) {
        cout << "Enter details of student " << loop + 1 << ":\n";
        std[loop].getDetails();
    }

    cout << endl;

    for (loop = 0; loop < n; loop++) {
        cout << "Details of student " << (loop + 1) << ":\n";
        std[loop].putDetails();
    }

    return 0;
}

解决方法

复制构造函数的工作原理类似于常规构造函数，但唯一的参数是对另一个相同类型对象的引用。在这种情况下，你应该在你的 CSStudent 类中创建一个带有签名的：

CSStudent(const CSStudent &other);

如果您希望它在赋值时命中，您还需要以类似的方式重载 = 运算符：

CSStudent& operator=(const CSStudent &other);

在这些构造函数中，您需要将数据从 other 复制到 this，然后在运算符重载中复制 return *this。您可以在 C++ 网站上找到更多信息：https://en.cppreference.com/w/cpp/language/copy_constructor

,

通常复制构造函数和复制赋值运算符具有以下签名。

class_name ( const class_name & )
class_name& operator = (const class_name &t)

在你的情况下，它会变成这样：

CStudent(const CStudent& other)
{
  strcpy (this->name,other->name);
  strcpy (this->specialty,other->specialty);
  this->facnum = other->facnum;
}

上面的代码将复制给定的 CStudent 但复制赋值运算符如下：

CStudent s = anotherCStudentObj;

复制赋值运算符在你的情况下很像复制构造函数，但除了在复制赋值运算符的末尾你应该添加 return *this。

示例：

CStudent& operator=(const CStudent& other)
{
  strcpy (this->name,other->specialty);
  this->facnum = other->facnum;
  return *this;
}

有关复制构造函数 here 的更多信息。

有关复制赋值运算符 here 的更多信息。

,

首先，请使用 std::string 而不是原始字符数组，这样更容易存储、修改和移动字符串数据：

    #include <string> // include string header
    
    std::string a = "Hello,world!" // explicit std namespace
    
    using namespace std;
    string b = "Hello,world!" // implicit std namespace

第二，你没有为类提供任何构造函数。构造函数是一种特殊的方法，以类名命名，没有返回类型：

    class CStudent {
    private:
        string name,specialty;
        int facnum;
    public:
        CStudent() = default; // default constructor
                              // with no parameters
        CStudent(string name,int facnum,string specialty) {
            this->name = name;
            this->facnum = facnum;
            this->specialty = specialty;
        } // constructor with specified parameters
        
        // copy constructor is a special constructor,// that receives a const class reference as it's parameter:
        CStudent(const CStudent& ref_obj) {
            this->name = ref_obj.name;
            this->facnum = ref_obj.facnum;
            this->specialty = ref_obj.specialty;
        }
    };

现在您可以像这样使用这些构造函数创建对象：

    CStudent a; // default constructed
    
    int facnum;
    string name,specialty; // set the data from console or manually
    CStudent b(name,facnum,specialty);
    CStudent b2 = CStudent(name,specialty); // the same
    auto b3 = CStudent(name,specialty); // also the same
    
    CStudent c(b); // copy constructed
    CStudent c2 = b; // the same

并且通常为类字段设置 setter/getter 是很常见的 setter/getter 是一种从字段中获取或设置数据的方法：

    // set of getters:
    string get_name() const {
        return name;
    }
    
    int get_facnum() const {
        return facnum;
    }
    
    string get_specialty() const {
        return specialty;
    }
    
    // set of setters:
    void set_name(string name) {
        this->name = name;
    }

    void set_facnum(int facnum) {
        this->facnum = facnum;
    }
    
    void set_specialty(string specialty) {
        this->specialty = specialty;
    }

现在我们可以创建一个函数，它会创建一个 CStudent 并从控制台设置它的数据：

    static CStudent GetFromConsole() {
        int facnum;
        string name,specialty;
        
        cout << "enter name: ";
        cin >> name;
        cout << "enter facnum:";
        cin >> facnum;
        cout << "Enter student speacialty: ";
        cin >> specialty;
        
        return CStudent(name,specialty);
    }

和一个方法，将数据打印到控制台：

    void PrintStudent() const {
        cout << "Name: " << name << endl;
        cout << "Fac. number: " << facnum << endl;
        cout << "Specialty: " << specialty << endl;
    }

,

一个工作示例

#include <iostream> // cout/cin
#include <string> // string container
#include <vector> // generic container

using namespace std;

class CStudent {
public:
    // Default constructor
    CStudent() = default;

    // Explicit constructor
    CStudent(string name,string specialty) {
        this->name = name;
        this->facnum = facnum;
        this->specialty = specialty;
    }

    // Copy constructor
    CStudent(const CStudent& obj) {
        this->name = obj.name;
        this->facnum = obj.facnum;
        this->specialty = obj.specialty;
    }

    // Method,that prints the contents of the object
    void PrintStudent() const {
        cout << "Name: " << name << endl;
        cout << "Fac. num: " << facnum << endl;
        cout << "Specialty: " << specialty << endl;
    }

private:
    string name;
    int facnum;
    string specialty;
};

// Function,that gets student data from the console
// and creates an instance of the CStudent class using this data
CStudent CreateFromConsole() {
    cout << "Enter name: ";
    string name;
    cin >> name;

    cout << "Enter fac. num: ";
    int facnum;
    cin >> facnum;

    cout << "Enter specialty: ";
    string specialty;
    cin >> specialty;

    cout << endl;
    return CStudent(name,specialty); // returns an instance of the class
}

int main() {
    vector<CStudent> students; // stack-like container

    cout << "Enter total number of students: ";
    int count;
    cin >> count;

    cout << "Enter details of students" << endl << endl;
    for (int i = 0; i < count; i++) {
        // Create an instance of the class
        CStudent student = CreateFromConsole();
        
        // Push a copy of the object into the container
        students.push_back(student);
    }

    cout << endl;

    cout << "Details" << endl << endl;
    for (int i = 0; i < students.size(); i++) {
        students[i].PrintStudent();
        cout << endl;
    }

    fflush(stdin); // Reset input console 
    getchar(); // Pause
    return 0;
}

,

抱歉，如果我来晚了，这里是复制赋值运算符和比较运算符示例：

class CStudent {
//         ...
//    the rest of the class
//         ...
private:
    void swap(CStudent& refObj) {                      // helper method,that would
        std::swap(this->name,refObj.name);            // swap data between two 
        std::swap(this->facnum,refObj.facnum);        // CStudent objects  
        std::swap(this->specialty,refObj.specialty);
    }

public:
    // copy assignment operator
    // allows to copy the data from one object
    // to an existing object
    // usage:
    //  CStudent a,b;
    //  // init a and b
    //  a = b; // a now holds a copy of the b's data 
    CStudent& operator=(const CStudent& refObj) {
        CStudent temp(refObj); // create a temporary copy
        this->swap(temp);      // swap the contents of this object and the copy
        return *this;          // return a reference to this object
                               
                               // after the method execution,the temp object
                               // that contains our old data will be destroyed
                               // this insures safe assignment,even if we assign
                               // the object to itself
    }
    
    // equality comparison operator
    // usage:
    //  CStudent a,b;
    //  // init a and b
    //  if (a == b) // the equality comparison operator is called
    //      cout << "Objects are equal\n";
    //  else
    //      cout << "Objects are not equal\n";
    //
    friend bool operator==(const CStudent& refA,const CStudent& refB) {
        return                                 // checks if
            refA.name == refB.name &&          // the names are equal AND
            refA.facnum == refB.facnum &&      // the fac.nums are equal AND
            refA.specialty == refB.specialty;  // the specialties are equal
    }
    // this is NOT a method,but a free function,// that is allowed to access private members and methods of the class
};