C++ 创建派生类对象时将参数传递给基类构造函数
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Pass Parameter to Base Class Constructor while creating Derived class Object
提问by CodeCrusader
Consider two classes Aand B
考虑两个类A和B
class A
{
public:
A(int);
~A();
};
class B : public A
{
public:
B(int);
~B();
};
int main()
{
A* aobj;
B* bobj = new bobj(5);
}
Now the class Binherits A.
现在该类B继承了A.
I want to create an object of B. I am aware that creating a derived class object, will also invoke the base class constructor , but that is the default constructor without any parameters.
我想创建一个对象B。我知道创建派生类对象也会调用基类构造函数，但这是没有任何参数的默认构造函数。
What i want is that Bto take a parameter (say 5), and pass it on to the constructor of A.
Please show some code to demonstrate this concept.
我想要的是B接受一个参数（比如 5），并将它传递给A. 请展示一些代码来演示这个概念。
回答by Bathsheba
Use base member initialisation:
使用基本成员初始化：
class B : public A
{
public:
B(int a) : A(a)
{
}
~B();
};
回答by SomeWittyUsername
B::B(int x):A(x)
{
//Body of B constructor
}
回答by Mandeep Singh
If you are using your derived class constructor just to pass arguments to base class then you can also do it in a shorter way in C++11:
如果您使用派生类构造函数只是将参数传递给基类，那么您也可以在 C++11 中以更短的方式进行：
class B : public A
{
using A::A;
};
Note that I have not even used "public" access specifier before it. This is not required since inherited constructors are implicitly declared with same access level as in the base class.
请注意，在它之前我什至没有使用过“公共”访问说明符。这不是必需的，因为继承的构造函数是隐式声明的，其访问级别与基类中的访问级别相同。
For more details, please refer to section Inheriting constructorsat: https://en.cppreference.com/w/cpp/language/using_declaration
有关更多详细信息，请参阅继承构造函数部分：https: //en.cppreference.com/w/cpp/language/using_declaration
Also you may refer to https://softwareengineering.stackexchange.com/a/307648to understand limitations on constructor inheritance.
您也可以参考https://softwareengineering.stackexchange.com/a/307648以了解构造函数继承的限制。
回答by Wilson
class A { public: int aval;
A类{公共：int aval;
A(int a):aval(a){};
~A();
};
};
class B : public A { public: int bval;
B 类：公共 A { 公共：int bval;
B(int a,int b):bval(a),A(b){};
~B();
};
};
int main() {
int main() {
B *bobj = new bobj(5,6);
//or
A *aobj=new bobj(5,6);
}
}
In this case you are assigning the values for base class and derived class .
在这种情况下，您正在为基类和派生类分配值。
