Class Accessor Methods...

[amac]

Is there a way to access a private member variable... so that to the user of the class it seems just to be a public const... but in actually fact its just a private member...

For example...

class X { // this class definition doesnt compile... just
private: // the best way to see what i am talkin about
int y;

public:
int y() { return this->y; }
};

X z;

cout << z.y; // this would display the contents of X::y.
z.y = 4; // this would be an error.

[parksie]

You don't need this->y -- just use y, since it assumes they'll be part of this.

class X {
public:
    int y() { return m_y; }
private:
    int m_y; // it's a good idea to prefix member variables
};

X z;

cout << z.y(); // it's a function call so you need the brackets
z.y() = 4; // this would be an error (obviously ;))

[HarryW]

Couldn't you use a member function to yield a pointer to the variable? Or actually, even better, a reference:

class X {
public:
    int& y() { return m_y; }
private:
    int m_y; // it's a good idea to prefix member variables
};

X z;

cout << z.y(); // it's a function call so you need the brackets
z.y() = 4; // would this still be an error?

[HarryW]

Seems to work fine. This compiled and ran as expected:

#include <iostream>

class X 
{
public:
    int& y() { return m_y; }
	X() { m_y = 2; }
private:
    int m_y; 
};

X z;

int main()
{
	std::cout << z.y() << std::endl; 
	z.y() = 4; 
	std::cout << z.y() << std::endl;

	return 0;
}

[parksie]

You could, but I think what he wanted was just to get the value...although returning a const reference is probably better if your class has a member variable that's a class/struct to prevent excess copying.

[HarryW]

Uhh maybe I'm having a blonde moment... why would that prevent excess copying?

[parksie]

Okay...if it returns a value, it copies it. If it returns a reference, it doesn't copy it. However, returning a reference means you can change it, which isn't wanted. Therefore you return a const reference.

[HarryW]

Ohh I was having a blonde moment. I didn't really understand what you were saying, I was thinking of the sentence in a different context.

I take the point about the const thing, I forgot it was meant to be const.

[HarryW]

Heh, yeah I just realised what you were talking about before you posted I thought you meant a const reference was better than a normal reference because it prevented copying... that's what confused me.

[parksie]

No problem...just a tad confusing

I suppose it's random things like this they want to fix in the new standard.

[HarryW]

I guess so. Have you heard anything specific about what they're looking at introducing? I read some general stuff but don't remember much of it.

[parksie]

Nothing specific, but according to those notes they're taking out the parts that confuse people.

[HarryW]

Heh, why didn't they think of that sooner?