英文:
How to initialize inherited values, and have abstract methods c++?
问题
这有点像一个问题中的多个问题。首先，C++ 中有没有一种方法可以初始化继承的值？换句话说，这就是我在 Java 中的意思：
// Class X
class X {
public:
int num;
X(int num) : num(num) {}
};
// Class Y
class Y : public X {
public:
Y() : X(5) {}
};
我的另一个问题是，我如何在 C++ 中创建一个抽象方法？同样，Java 示例：
// Class X
class X {
public:
int num;
X(int num) : num(num) {}
virtual void use() = 0;
};
// Class Y
class Y : public X {
public:
Y() : X(5) {}
void use() override {
}
};
谢谢。
英文:
This is kinda multiple questions in a single question. First off, is there a way to initialize inherited values in C++? In other words, this is what I mean in java :
// Class X
public class X {
int num;
public X(int num) {
this.num = num;
}
}
//Class Y
public class Y extends X{
public Y() {
super(5);
}
}
My other question is how would I create an abstract method in C++?
Again, java example :
// Class x
public abstract class X {
int num;
public X(int num) {
this.num = num;
}
public abstract void use();
}
// Class y
public class Y extends X{
public Y() {
super(5);
}
@Override
public void use() {
}
}
Thanks.
答案1
得分: 2
首先：您想了解初始化列表。对于您的第一个代码片段，适当的代码应为
class X {
int num;
public:
X(int t_num) : num(t_num) { } // 我们可以使用初始化列表来设置成员变量
};
class Y : public X {
public:
Y() : X(5) { } // 在构造函数的主体中不需要有任何内容
};
对于第二个问题，在C++中，您可以在不提供定义的情况下声明函数，这与Java中定义抽象函数非常相似。如果您的目的是进行运行时多态性，您还需要将它们声明为虚函数：
class X {
int num;
public:
virtual void use() = 0; // = 0 表示在X中没有实现
};
class Y : public X {
void use() override { } // 不需要重新声明虚函数
// override 关键字不是必需的，但可以澄清语义
};
英文:
First: You want to learn about initializer lists. For your first code snippet, the appropriate code would be
class X {
int num;
public:
X(int t_num) : num(t_num) { } // We can use initializer lists to set member variables
};
class Y : public X {
public:
Y() : X(5) { } // No need to have anything in the body of the constructor
};
For the second, in C++ you can always declare functions without providing a definition, which is very similar to defining an abstract function in Java. If your intent is to do run-time polymorphism, you'll also want to make them virtual functions:
class X {
int num;
public:
virtual void use() = 0; // The = 0 indicates there's no implementation in X
};
class Y : public X {
void use() override { } // No need to redeclare virtual
// override keyword not necessary but can be clarifying
};
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