How Can C Objects of the Same Class Access Each Other's Private Member Variables?

Why Can Objects of the Same Class Access Each Other's Private Data?

In C , objects of the same class can access each other's private data because access control operates on a per-class, not per-object, basis. This means that private data is only inaccessible to objects outside of the class.

For example, consider the following code:

class TrivialClass {
public:
  TrivialClass(const std::string& data) : mData(data) {}

  const std::string& getData(const TrivialClass& rhs) const {
    return rhs.mData;
  }

private:
  std::string mData;
};

int main() {
  TrivialClass a("fish");
  TrivialClass b("heads");

  std::cout << "b via a = " << a.getData(b) << std::endl;
  return 0;
}

In this code, TrivialClass has a private member variable mData and a public member function getData that returns a reference to mData. When objects a and b are created, they are both able to access each other's private data through the getData function.

This is possible because C 's access control is based on the following rules:

• Public members are accessible from anywhere.
• Private members are accessible only from within the class.
• Protected members are accessible from within the class and from derived classes.

Since mData is a private member, it should only be accessible from within the TrivialClass class. However, because access control is per-class, objects of the same class can still access each other's private members.

This behavior is not present in all programming languages. Some languages, such as Java, have true per-object access control, which means that objects of the same class cannot access each other's private data.

The above is the detailed content of How Can C Objects of the Same Class Access Each Other's Private Member Variables?. For more information, please follow other related articles on the PHP Chinese website!