尝试访问基类的受保护数据成员时发生编译错误？

Question

So I have a class address, a class name, and a class person that is derived from name.

class address
{
     public:
     address(char * street, char * zip);

     protected:
     char * street;
     char * zip;
};
class name
{
     public: 
     name( char * initial_name);

     protected:
     char * name;
     address a_address;
};
class person : public name
{
     public:
     person(char * name, char * street, char * zip);
}

the compile error is when I define the person constructor, it looks like this:

person::person(char * initial_name, char * street, char * zip): 
name(initial_name)
{
   a_address.address(street, zip);
}

when I try to access a_address it's telling me invalid use of address::address. Any clues to what I'm doing wrong? Thanks

Answer 1

the compile error is when I define the person constructor,

You have a naming confusion here. You have a class called name which has a member called name . It has nothing to do with protected access to the member variable name in class name . You may want to change the variable to a_name or something else that is different than name .

access a_address it's telling me invalid use of address::address

You cannot call a constructor on an object. That's what you are attempting to do with:

a_address.address(street, zip);

You need to create an appropriate constructor in name and pass the arguments from person to name .

Here's an updated version of your posted code that compiles and builds for me.

class address
{
   public:
      address(char * street, char * zip) : street(street), zip(zip) {}

   protected:
      char * street;
      char * zip;
};
class name
{
   public: 
      name(char * initial_name, char * street, char * zip);

   protected:
      char * a_name;
      address a_address;
};

name::name(char * initial_name, char * street, char * zip) :
      a_name(initial_name), a_address(street, zip)
{
}

class person : public name
{
   public:
      person(char * initial_name, char * street, char * zip);
};

person::person(char * initial_name, char * street, char * zip) : 
      name(initial_name, street, zip)
{
}

int main() {}

Answer 2

Your name class has a member variable named name . Your code doesn't compile here because of that.

Also, your person class needs a semicolon after the class declaration.

And you could set a_address like this:

a_address = address(street, zip);

Answer 3

You can access the member variable a_address , as it is protected in the base class; but you cannot access the member variables inside the class address , as you did not derive from address . For the class address , you are a stranger, and you have no access to its protected members.

Your structure is not very object oriented, that's why you run into such troubles. The class address should have a constructor, which you call with its details, and address itself handles the assignemnets to its internal members. If you access members from outside the class, you use them only as simple data structures. That is fine, but it is not object oriented coding, and if you want to work that way , you should change class to struct (as this is exactly the difference between the two), and remove the protected.