Question

在我的程序中，我有几个不同的类，它们包含一个具有相同名称但输出不同的函数：

#include <iostream>

#define CLASS_TO_USE C

class A{
public:
    std::string class_name = "Class A";

    A()
    {};

    double add(const double a, const double b) const
    {
        return a + b;
    }
};

class B{
public:
    std::string class_name = "Class B";

    B()
    {};

    double add(const double a, const double b) const
    {
        return 2 * a + b;
    }
};


class C{
public:
    std::string class_name = "Class C";

    C()
    {};

    double add(const double a, const double b) const
    {
        return 3 * a + b;
    }
};

template <class T>
void calculate_addition(const T &local_class, const double a, const double b)
{
    std::cout << "Addition gives the value " << local_class.add(a, b) << '\n';
}

int main()
{
    CLASS_TO_USE local_class;
    std::cout << "Hello World!" << std::endl;
    calculate_addition(local_class, 2, 3);
    return 0;
}

当前，我通过更改CLASS_TO_USE的变量在这些类之间切换，但是该方法需要重新编译，这需要一些时间。相反，我更喜欢一种在运行时有效的方法，即可以在其中使用f.ex的方法。用户的输入。有可能吗？如果可以，怎么办？

编辑：我使用以下代码解决了问题：

#include <iostream>
#include <variant>

class A{
public:
    std::string class_name_string = "Class A";

    A()
    {};

    virtual double add(const double a, const double b) const
    {
        (void) a;
        (void) b;
        return 0;
    };

    virtual std::string class_name(void) const
    {
        return class_name_string;
    }
};

class B : public A{
public:
    std::string class_name_string = "Class B";

    B()
    {};

    double add(const double a, const double b) const
    {
        return 2 * a + b;
    }

    virtual std::string class_name(void) const
    {
        return class_name_string;
    }
};


class C : public A{
public:
    std::string class_name_string = "Class C";

    C()
    {};

    double add(const double a, const double b) const
    {
        return 3 * a + b;
    }

    virtual std::string class_name(void) const
    {
        return class_name_string;
    }
};

class D : public A{
public:
    std::string class_name_string = "Class D";

    D()
    {};

    double add(const double a, const double b) const
    {
        return a + b;
    }

    virtual std::string class_name(void) const
    {
        return class_name_string;
    }
};

void calculate_base_addition(const A &local_class, const double a, const double b)
{
    std::cout << "Addition gives the value " << local_class.add(a, b) << " by using " << local_class.class_name() << '\n';
}

int main()
{
    A *base_class;
    B tmp_class_B;
    C tmp_class_C;
    D tmp_class_D;
    int class_to_choose = 2;
    switch(class_to_choose)
    {
    case 0:
    {
        base_class = &tmp_class_B;
        break;
    }
    case 1:
    {
        base_class = &tmp_class_C;
        break;
    }
    case 2:
    default:
    {
        base_class = &tmp_class_D;
        break;
    }
    }
    std::cout << "Name of base_class: " << (*base_class).class_name() << '\n';
    std::cout << "Name of derived class: " << tmp_class_B.class_name() << '\n';
    std::cout << "Hello World!" << std::endl;
    calculate_base_addition(*base_class, 2, 3);
    return 0;
}

，并在此处提出后续问题：Define class variable in class based on user input

Answer 1

您可以分派整数用户输入，例如像这样：

(bCompleted) in
    if (bCompleted) {

         UIView.animate(withDuration: 1.5, animations: {
             book1ImageViewI.layer.transform = CATransform3DRotate(transform, -.pi/2, 0, 1, 0)
             book1ImageViewI.image = UIImage(named:"0a6752b7cd35fc441c1528ee5078384d--antique-books-rabbit-holer.png")
             }, completion: {
                 (bFinished) in
                 //Whatever
         })
    }

根据C ++中的外部输入选择类

1 个答案: