为什么我会收到错误“使用已删除的函数'class :: class()”

Question

#include <iostream>
using namespace std;

class student
{
protected:
    string name;
    int roll;
    int age;
public:
    student(string n, int r, int a)
    {
        name = n;
        roll = r;
        age = a;
    }
};

class test : public student
{
protected:
    int sub[5];
public:
    void marks()
    {
        cout << "Enter marks in 5 subjects: " << endl;
        cin >> sub[0] >> sub[1] >> sub[2] >> sub[3] >> sub[4];
    }
    void display()
    {
        cout << "Name : " << name << "\nRoll number : " << roll << "\nAge: " << age << endl;
        cout << "Marks in 5 subjects : " << sub[0] << ", " << sub[1] << ", " << sub[2] << ", " << sub[3] << ", " << sub[4] << endl;
    }
};

class sports
{
protected:
    int sportmarks;
public:
    sports(int sm)
    {
        sportmarks = sm;
    }
};

class result : public test, public sports
{
    int tot;
    float perc;
public:
    void calc()
    {
        tot = sportmarks;
        for(int i = 0; i < 5; i++)
            tot = tot + sub[i];
        perc = (tot / 600.0) * 100;
        cout << "Total: " << tot << "\nPercentage: " << perc << endl;
    }
};

int main()
{
    student ob1("Name", 781, 19);
    sports ob2(78);
    result ob;
    ob.marks();
    ob.display();
    ob.calc();
}

有人要求我使用参数化构造函数来解决这个问题，并注意到我在使用构造函数时遇到了这些错误。如果这篇文章不方便阅读，请见谅。从参数化构造函数创建对象时，我可以通过什么方式运行此代码？

use of deleted function 'result::result()'
use of deleted function 'test::test()'.
no matching function for call to 'student::student()'
no matching function for call to 'sports::sports()'

Answer 1

student 和 sports 具有用户定义的构造函数，因此编译器不会为它们生成默认构造函数。

test 和result 没有用户定义的构造函数，因此编译器将为它们生成默认构造函数。但是，由于student 和sports 没有默认构造函数，因此生成的默认构造函数被标记为delete'd，因为它们不可用。这就是你得到错误的原因。

要使您的main() 按原样编译，您需要为test 和result 定义自己的默认构造函数，它们将显式参数值传递给它们的基类，例如：

#include <iostream>
using namespace std;

class student
{
protected:
    string name;
    int roll;
    int age;
public:
    student(string n, int r, int a)
    {
        name = n;
        roll = r;
        age = a;
    }
};

class test : public student
{
protected:
    int sub[5];
public:
    test() : student("", 0, 0) {}

    void marks()
    {
        cout << "Enter marks in 5 subjects: " << endl;
        cin >> sub[0] >> sub[1] >> sub[2] >> sub[3] >> sub[4];
    }

    void display()
    {
        cout << "Name : " << name << "\nRoll number : " << roll << "\nAge: " << age << endl;
        cout << "Marks in 5 subjects : " << sub[0] << ", " << sub[1] << ", " << sub[2] << ", " << sub[3] << ", " << sub[4] << endl;
    }
};

class sports
{
protected:
    int sportmarks;
public:
    sports(int sm)
    {
        sportmarks = sm;
    }
};

class result : public test, public sports
{
    int tot;
    float perc;
public:
    result() : test(), sports(0) {}

    void calc()
    {
        tot = sportmarks;
        for(int i = 0; i < 5; i++)
            tot = tot + sub[i];
        perc = (tot / 600.0) * 100;
        cout << "Total: " << tot << "\nPercentage: " << perc << endl;
    }
};

int main()
{
    student ob1("Name", 781, 19);
    sports ob2(78);
    result ob;
    ob.marks();
    ob.display();
    ob.calc();
}

Online Demo

但是，这不是很有用，所以我建议调整 result 的构造函数以获取您事先已经创建的 student 和 sports 对象，并将它们传递给基类复制构造函数，这编译器会为你生成，例如：

#include <iostream>
using namespace std;

class student
{
protected:
    string name;
    int roll;
    int age;
public:
    student(string n, int r, int a)
    {
        name = n;
        roll = r;
        age = a;
    }
};

class test : public student
{
protected:
    int sub[5];
public:
    test(const student &s) : student(s) {}

    void marks()
    {
        cout << "Enter marks in 5 subjects: " << endl;
        cin >> sub[0] >> sub[1] >> sub[2] >> sub[3] >> sub[4];
    }

    void display()
    {
        cout << "Name : " << name << "\nRoll number : " << roll << "\nAge: " << age << endl;
        cout << "Marks in 5 subjects : " << sub[0] << ", " << sub[1] << ", " << sub[2] << ", " << sub[3] << ", " << sub[4] << endl;
    }
};

class sports
{
protected:
    int sportmarks;
public:
    sports(int sm)
    {
        sportmarks = sm;
    }
};

class result : public test, public sports
{
    int tot;
    float perc;
public:
    result(const student &s, const sports &sp) : test(s), sports(sp) {}

    void calc()
    {
        tot = sportmarks;
        for(int i = 0; i < 5; i++)
            tot = tot + sub[i];
        perc = (tot / 600.0) * 100;
        cout << "Total: " << tot << "\nPercentage: " << perc << endl;
    }
};

int main()
{
    student ob1("Name", 781, 19);
    sports ob2(78);
    result ob(ob1, ob2);
    ob.marks();
    ob.display();
    ob.calc();
}

Online Demo