Accessing private members [closed]

Answer 1

I have had this happen to me since there was a very crappy source control system in place where for old versions of the application making changes to header files was pretty much impossible.

If some cases you just need to do a hack.

In the source file from which you need to access the private data member you can put in this as a first line:

#define private public
#define protected public

and access anything you want.

Answer 2

Ah, abstraction - you can't live without it and yet it is so painful to deal with sometimes :)

Anyway, ethics aside, what if the "owner" of the class decides to change the internal implementation, or simply reverses the order of the private data members?

Answer 3

"Never say never". I'm sure somewhere in the universe, there's a situation that will force you to have to do this...

But I certainly would cringe if I had to do it. You truly need get lots of opinions on your situation before pulling the trigger. Can you describe your specific situation and maybe we could see if it makes sense or what better alternatives might exist?

In response to comment/question-- Define "permissions" -- institutional permission? That sounds like not a programming problem, but something to talk to whoever is asserting said permission. Maybe this is more of a political issue than a technical one? Again, I think we need more specifics--even if it was somewhat about the politics of the situation. That may or may not be deemed out of scope for the website, however.

Answer 4

Simple answer: No.

It is not ethical and it will turn into a maintenance nightmare at some point. The internal private members of a library can change and break your code. Developers of the library do not need to know (nor want to) that you are violating the encapsulation.

Classes usually have invariants over their methods that some times will not be documented, but accessing and changing the values from the outside can break those invariants. As an example, if you change the reserved space in a vector for a higher value, the vector will not allocate new space until it has filled the existing and that won't happen before hitting unallocated memory: your application will crash.

If the attribute is private, it is not for you to use it, only for the class itself or the the class' friends that know about the member, how to use it, how not to break it. If the programmer wanted you to change the field, it would be public.

Answer 5

I'm not sure that "ethics" really come into it. It busts the heck out of encapsulation though.

EDIT: I would almost never accept this if I were performing a code review. You'd have to work really hard to convince me there's no way of designing around the need for this. It's possible you'd succeed, but there'd have to be major warnings all over the place, and rock hard unit tests to make sure that if anything changed to break it, you'd know quickly.

Answer 6

If you feel the urge to do this, forget casting - just modify the class declaration in the header file:

class A {
  private:
    int x;
};

change that to:

class A {
  public:
    int x;
};

and you are good to go. Well, perhaps "good" is not quite the right word.