我很困惑:我认为 protected 数据是C++中给定类的子级可以读取/写入的。
下面的代码片段无法在MS Compiler中编译
class A
{
protected:
int data;
};
class B : public A
{
public:
B(A &a)
{
data = a.data;
}
};
int main()
{
A a;
B b = a;
return 0;
}
错误信息:
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 15.00.30729.01 for 80x86
Copyright (C) Microsoft Corporation. All rights reserved.
demoFail.cpp
demoFail.cpp(12) : error C2248: 'A::data' : cannot access protected member declared in class 'A'
demoFail.cpp(4) : see declaration of 'A::data'
demoFail.cpp(2) : see declaration of 'A'
我究竟做错了什么?
最佳答案
根据TC++ PL,第404页:
当然,这是为您的情况解决此问题的简单方法:
class A
{
protected:
int data;
};
class B : public A
{
public:
B(const A &a)
: A(a)
{
}
};
int main()
{
A a;
B b = a;
return 0;
}