Friend Functions in Namespaces.

[Sam Finch]

I'm having a bit of a declarations Problem and I can't seem to get the right order of declarations.

I have a class, "DisplayTree" which represents various things to be drawn on an HDC.


The DisplayTrees are Drawn using an array of functions
DrawDisplayTreeFunctions[] which are not part of the class but are friends with it. And as I need lots of seperate functions to fill the Array I'd rather stow them all away in a namespace.

So Far So Good, I just do this.

//Declarations of array Functions in a Namespace
namespace nDrawDisplayTreeFunctions
{

    void ArrayFunction1(void);
    void ArrayFunction2(void);
    void ArrayFunction3(void);
    void ArrayFunction4(void);
    void ArrayFunction5(void);

}

//Function Array With Functions In it
void (* DrawDisplayTreeFunctions[]) (void) = 
{
        nDrawDisplayTreeFunctions::ArrayFunction1,
        nDrawDisplayTreeFunctions::ArrayFunction2,
        nDrawDisplayTreeFunctions::ArrayFunction3,
        nDrawDisplayTreeFunctions::ArrayFunction4,
        nDrawDisplayTreeFunctions::ArrayFunction5
};




class DisplayTree
{


    friend void nDrawDisplayTreeFunctions::ArrayFunction1(void);
    friend void nDrawDisplayTreeFunctions::ArrayFunction2(void);
    friend void nDrawDisplayTreeFunctions::ArrayFunction3(void);
    friend void nDrawDisplayTreeFunctions::ArrayFunction4(void);
    friend void nDrawDisplayTreeFunctions::ArrayFunction5(void);


     //Other class members

};


namespace nDrawDisplayTreeFunctions
{

    void ArrayFunction1(void)
    {

        //Function definition

    }


    void ArrayFunction2(void)
    {

        //Function definition

    }


    void ArrayFunction3(void)
    {

        //Function definition

    }


    void ArrayFunction4(void)
    {

        //Function definition

    }


    void ArrayFunction5(void)
    {

        //Function definition

    }

}

And That's all Lovely The Array Functions can get at the protected members of the class and they're all tucked away in a namespace where they can't be called willy nilly.

The trouble is I want the functions to take a *DisplayTree as a parameter. Which causes problems, because I have to Declare the Functions inside the namspace before I define the class so I can make them friends. And I have to declare the class before I declare the functions So they can take a *DisplayTree as a Parameter. Can Anyone see a way around this Problem?

help.

[parksie]

Why not put a

class DisplayTree;

at the top? That will tell the compiler that there is code for that, but it can't have it just yet.

[Sam Finch]

Thanks parksie.

I didn't realise yu could do that for classes.

[amac]

what is the advantage of using namespaces?

[kedaman]

namespaces will keep your code organized, but mostly theyre good for preventing name collisions between included files.

[parksie]

See the STL. For example, whenever anyone uses something from the STL, you often see "using namespace std;". You shouldn't really do that but it's okay for .cpp files. However, you should never import a whole namespace into a header file. If you use it in a source file the names are only imported for that file so you can keep track easier.