C++: error: 'int X::secret' is private within this context

Meaning

Members of a class are private by default; a struct defaults to public. Access is checked by the name's declaration, not by the object, so even a getter named differently is the fix. Friends and member functions of the same class are exempt.

Common causes

• Accessing a private data member from main or another class
• Inheriting privately (the default for class D : B) and converting to the base
• Forgetting public: after the first member of a class
• Protected member accessed through a base-class object instead of this

Detailed fix by platform

Code examples

class Account {
    int balance_ = 0;                     // private by default
public:
    int balance() const { return balance_; }
    void deposit(int n) { balance_ += n; }
};

int main() {
    Account a;
    // a.balance_ = 5;                    // error: 'int Account::balance_' is private within this context
    a.deposit(5);
    return a.balance();
}

How to diagnose

1. Access — Is the member private, protected or public?
2. Inheritance — class or struct, public or private?
3. Caller — Is the code inside the class or a friend?

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