Using Friends keyword... appropriate?

**Iamien** · 06-04-2005

For a class i am currently designing, called Pane, during a method i am using another pane to calculate my abs left and top coordinates.

my absLeft = parent.absLeft;

Would it be appropriate to make Pane a friend to Pane, so i could just access this directly, or would it be more appropriate to use a method to return the value.

**hk_mp5kpdw** · 06-04-2005

Post the class interface and the code for the function that is performing this calculation please.

**Shakti** · 06-04-2005

if your class is something similar to this:

Code:

class A
{
private:
    int someNum;
public:
    void DoSomething(A foo)
    {
        // Do some stuff
    }
};

and you want A::DoSomething(A foo) to have access to someNum in foo it already has that. Every instance of a class can access all memberdata in an instance if they are of the same class. This means you can safely do this

Code:

class A
{
private:
    int someNum;
public:
    void DoSomething(A foo)
    {
        someNum = foo.someNum
    }
};

**Iamien** · 06-04-2005

I ended up just making functions because i wasnt sure.

Code:

Interface:
#include "SDL.h"
#include <vector>
using std::vector;



class Pane
{
private:
	int top,left,level;
	vector<Pane> * children; // Pointers to Children
	Uint32 color;
	Pane * parent;
	int absLeft, absTop;
	int drawTestLeft, drawTestTop;
public:
	void setTop( int );
	void SetLeft( int );
	void setLevel( int );
	void setColor( Uint32 );
	void setParent( Pane & );
	void getParent( Pane * );

	int getAbsLeft();
	int getAbsTop();
	void draw();
	Pane();


};

Function

void Pane::setParent(Pane & p)
{
	if ( &p != NULL )
	{
		this->parent = &p;
		this->absLeft = p.getAbsLeft() + this->left;
		this->absTop = p.getAbsTop() + this->top;
		
	}
	
}

**Iamien** · 06-04-2005

just saw your post Shakti. i never knew, good to know, thanks

**Thantos** · 06-04-2005

btw:
this->
is unneeded as it's implied. So you could have:

Code:

parent = &p;
absLeft = p.getAbsLeft() + left;
absTop = p.getAbsTop() + top;

**okinrus** · 06-04-2005

Would it be appropriate to make Pane a friend to Pane, so i could just access this directly, or would it be more appropriate to use a method to return the value.

Iamian, you don't need to use friends in this situation. In fact, you don't have to use anything but direct access. Within Pane::setParent, p and "this" are of the same class. What you want for your clases is to use only public methods for the behavior that other classes use. Sometimes you need to use friends but the cases are rare. Two common cases are operator overloading and implicit types(ie., you're writing a Complex number class, overloading operator+, and want to be able to write 5 + Complex(3, 4) and have the 5 implicitly convert to a complex numbe) and iterators.

**Iamien** · 06-04-2005

Thanks for all your responces..
Educational

**Iamien** · 06-05-2005

I come back with another question
I want to make a class in my project, to function as an "Artist" i plan to pass this class around to difference objects to have it draw them. Should i make him Friends with the classes? so that i can avoid the overhead in calling functions to get the variables <or should i inline the functions>
there would be about 4 function calls per object, each time it was drawn. everything that has to be drawn will be drawn so i believe it's an O(n)
Any advice or suggestions would be great

**okinrus** · 06-05-2005

want to make a class in my project, to function as an "Artist" i plan to pass this class around to difference objects to have it draw them. Should i make him Friends with the classes? so that i can avoid the overhead in calling functions to get the variables <or should i inline the functions>

The function overhead can be mitigated by using inline functions. But for using friends the way you've outlined, I can't think of a situation. Probably better off using a "struct" and having all the data public than using a lot of friends.

there would be about 4 function calls per object, each time it was drawn. everything that has to be drawn will be drawn so i believe it's an O(n)

Retrieving the data from the classes is usually so fast compared to the io drawing functions that it's usually a non-issue.

**Iamien** · 06-06-2005

Alright thanks

Thread: Using Friends keyword... appropriate?

Thread Tools

Search Thread

Display

Using Friends keyword... appropriate?

Similar Threads

template keyword needed

keyword replacement

Virtual Keyword

'new' keyword

how to search a keyword in C?