Question

I am learning C++, and I’m trying to learn more about using the friend keyboard.

However, I am having trouble using nested classes in my Header file.

I know that header files should only be used for declarations but I didnt want to include a cpp file with it so I just used a header file to declare and build.

Anways, I have a main.cpp file that I want strictly to be used for creating objects of classes and accessing its functions.

However, I dont know exactly how to create the FriendFunctionTest function in my header file to where I can access it in my main.cpp source file using the header Class object because I’m trying to understand the “friend” keyword.

Here is my header code:

#ifndef FRIENDKEYWORD_H_
#define FRIENDKEYWORD_H_

using namespace std;

class FriendKeyword
{
    public:
        FriendKeyword()
        {//default constructor setting private variable to 0
            friendVar = 0;
        }
    private:
        int friendVar;

    //keyword "friend" will allow function to access private members
    //of  FriendKeyword class
    //Also using & in front of object to "reference" the object, if
    //using the object itself, a copy of the object will be created
    //instead of a "reference" to the object, i.e. the object itself
    friend void FriendFunctionTest(FriendKeyword &friendObj);
};

void FriendFunctionTest(FriendKeyword &friendObj)
{//accessing the private member in the FriendKeyword class
    friendObj.friendVar = 17;

    cout << friendObj.friendVar << endl;
}

#endif /* FRIENDKEYWORD_H_ */

In my main.cpp file, I wanted to do something like this:

FriendKeyword keyObj1;
FriendKeyword keyObj2;
keyObj1.FriendFunctionTest(keyObj2);

But obviously its not going to work since the main.cpp cant find the FriendFunctionTest function in the header file.

How do I fix this issue?

And I apologize again, I’m just trying to learn C++ online.

Answer 1

The friend keyword is only used to specify if a function or other class can have access to the private members of that class. You have no need for class inheritance or nesting because FriendFunctionTest is a global function. Global functions do not require any class prefixes when invoked.

Source for friend: http://msdn.microsoft.com/en-us/library/465sdshe(v=vs.80).aspx