Thread: Why can friend operators be public or private?

EDIT: If I had more space for the thread title, it should've been entitled:

"Why doesn't it matter if friend operators are public or private?"

I know the friend keyword gives a class or function access to a classes private data, but i'm confused about how they behave with it's calling class.
I mean, if a function/operator/class is in the private section, I shouldn't be allowed to access it outside the class right?


Given the following example:

Code:

class Test{
	
	public:
	
		friend bool operator==( const Test& lhs, const Test& rhs ){
			
			return lhs.data == rhs.data;
		};
		
		friend bool operator!=( const Test& lhs, const Test& rhs ){
			
			return lhs.data != rhs.data;
		};
		
	public:
	
		Test( int d ) : data( d ) {};
		
	private:
	
		int data;
};

int main(){
	
	Test a( 1 );
	
	Test b( 2 );
	
	if( a != b ){
		
		std::cout << "A and B are NOT equal.\n";
	}
	
	return 0;
}

It makes no difference whether or not the overloaded operators are in the public or private sections.

1) Is that true? Or is there more testing that can prove otherwise?

2) If it doesn't make a difference, why doesn't it make a difference?

Thanks in advance

Code:

class Test{
	
	private:
	
		friend bool operator!=( const Test& lhs, const Test& rhs ){
			
			return lhs.data != rhs.data;
		};
		
	public:
	
		Test( int d ) : data( d ) {};
		
	private:
	
		int data;
};

class TestChild : public Test{
	
	public:
	
		TestChild( int d ) : Test( d ) {};
};

class TestUnrelated{
	
	public:
	
		TestUnrelated( int d ) : m_Test( new Test( d ) ) {};
		
        private:

		friend bool operator!=( const TestUnrelated& lhs, const TestUnrelated& rhs ){
		
			return lhs.m_Test != rhs.m_Test;
		};
		
	private:
	
		Test* m_Test;
};

int main(){
	
	TestChild a( 1 );
	TestChild b( 2 );
	
	if( a != b )
		std::cout << "A and B are NOT equal.\n";
	
	TestUnrelated c( 5 );
	TestUnrelated d( 6 );
	
	if( c != d )
		std::cout << "C and D are NOT equal.\n";
	
	return 0;
}

And it holds true for in all the cases I have above. The behavior is as I should've expected. Anyway thanks for your help on such a dumb question.

Originally Posted by dudeomanodude

[code]And it holds true for in all the cases I have above. The behavior is as I should've expected. Anyway thanks for your help on such a dumb question.

It's not a dumb question. It's the kind of thing I've never seen asked here before and others may well read this thread and think "oh that's why".

One thing to note though, you don't need a semi-colon after the closing brace of a function. You only need that after the closing brace of the class definition.