c++ - 取决于var类型的if循环

假设我要这样做:

type variable;

if(condition1){
 variable=  something of class A
}
else if(condition2){
 variable = something of class B
}

do more with / variable

我该如何实现？

最佳答案

只要您的A和B类具有相同的基础，就可以使用指针进行类似的操作。像这样:

class Base {
    //...
public:
    virtual ~Base() {} // MUST have VIRTUAL member for dynamic_cast
};

class A : public Base {
    //...
public:
    virtual ~A() {}
};

class B : public Base {
    //...
public:
    virtual ~B() {}
};

    // ...
    bool condition = true;
    Base* variable;
    if (condition)
        variable = new A;
    else
        variable = new B;
    //...

一旦创建了类对象(并提供了至少一个虚函数)，您就可以在后面的代码中使用 dynamic_cast 运算符“询问”它实际上是哪种类型的对象:

    // ... continuing in the same scope as the previous code...
    if (dynamic_cast<A*>(variable) != nullptr) { // Points to an A object:
        // Do something specific to A
    //  A* ptrA = dynamic_cast<A*>(variable);
    //  ptrA->member = value;
    }
    else if (dynamic_cast<B*>(variable) != nullptr) { // Points to a B object:
        // Do something specific to B
    }
    else { // Not an A or a B...
        // (error handling?)
    }
    //...
    // And, of course, don't forget to free the object when finished:
    delete variable;

关于c++ - 取决于var类型的if循环，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/61211394/