我有一个基类,它有一个需要一个参数(字符串)的构造函数。然后我有一个派生类,它也有自己的构造函数。我想实例化派生类,并能够设置基类构造函数的参数。
class BaseClass {
public:
BaseClass (string a);
};
class DerivedClass : public BaseClass {
public:
DerivedClass (string b);
};
int main() {
DerivedClass abc ("Hello");
}
我不知道在调用派生类时如何设置基类构造函数的参数。
您有两种可能性-内联:
class DerivedClass : public BaseClass {
public:
DerivedClass (string b) : BaseClass(b) {}
};
或越界:
class DerivedClass : public BaseClass {
public:
DerivedClass (string b);
};
/* ... */
DerivedClass::DerivedClass(string b) : BaseClass(b)
{}
更多示例:
class DerivedClass : public BaseClass {
public:
DerivedClass(int a, string b, string c);
private:
int x;
};
DerivedClass::DerivedClass(int a, string b, string c) : BaseClass(b + c), x(a)
{}
在初始值设定项列表上:
class MyType {
public:
MyType(int val) { myVal = val; } // needs int
private:
int myVal;
};
class DerivedClass : public BaseClass {
public:
DerivedClass(int a, string b) : BaseClass(b)
{ x = a; } // error, this tries to assign 'a' to default-constructed 'x'
// but MyType doesn't have default constructor
DerivedClass(int a, string b) : BaseClass(b), x(a)
{} // this is the way to do it
private:
MyType x;
};
如果你只想从一个传递给基类构造函数的参数中构造一个派生类实例,你可以这样做:
C++03(我添加了显式,并通过常量引用传递):
class DerivedClass : public BaseClass {
public:
explicit DerivedClass (const std::string& b) : BaseClass(b) {}
};
C++11(获取所有基类构造函数):
class DerivedClass : public BaseClass {
public:
using BaseClass::BaseClass;
};
如果你想调用不同的DerivedClass
构造函数,并将BaseClass
构造函数调用为其他值,你也可以这样做:
class DerivedClass : public BaseClass {
public:
explicit DerivedClass () : BaseClass("Hello, World!") {}
};
使用此
DerivedClass::DerivedClass(string b)
: BaseClass(b)
{
}
只需将参数直接传递给基类构造函数