CODEWITHSUNDEEP
c++oop
user360907
user360907

Reputation:

Why can my object not access it's own private member variable? [C++]

I have a class called class Car, which has be instantiated as the object Car car1. One of the member variables of Car is Car::width, but when I try to execute the line

cout << car1.width << endl;

from main() I am told that this is not possible because Car::width is private. It was my understanding that private members could be accessed by the objects of the class to which they belong, but this situation has me completely stumped. What's the deal with private members being accesses by their own objects?

Upvotes: 4

Views: 5164

Answers (6)

Steve Townsend
Steve Townsend

Reputation: 54178

If the accessing function (main in this case) is not a member or friend of your class Car, then the compiler is correct in saying that private member width is off-limits in this context.

When you think about it, if anybody who could create a Car could access its private members, privacy would not mean very much. You make the constructor public to allow creation of the object, but hide the created object's data members from such users to properly encapsulate them. You limit the manipulation of the class's private internals to what's allowed by legal usage of the class's public or protected members.

Upvotes: 2

John Dibling
John Dibling

Reputation: 101494

cout << car1.width

This isn't car1 trying to get to width -- it's cout trying to get to width. cout isn't a member of car1 so since width is private, it fails.

Upvotes: -1

Graeme Perrow
Graeme Perrow

Reputation: 57278

A method on class Car can access the width member, but your code (the one doing the cout) cannot.

Upvotes: 0

Mario
Mario

Reputation: 393

It can be accessed from within a member function, not outside like you have it here. The whole point of a private variable is to prevent exactly what you are trying to do, namely disallow users of the class to use the member variable.

Upvotes: 2

valdo
valdo

Reputation: 12951

Car can access width. But in your example it's you who's trying to access width. This is exactly the meaning of private.

Upvotes: 2

zvrba
zvrba

Reputation: 24584

Private members are accessible by the methods of the same class to which they belong.

Upvotes: 6

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