CODEWITHSUNDEEP
c++multithreadingclassprivate
Dimitry
Dimitry

Reputation: 85

C++ Private mutex access

In book "C++ Concurrency in Action: Practical Multithreading" by Anthony Williams I found this code example 

template<typename T>
class threadsafe_stack
{
private:
    std::stack<T> data;
    mutable std::mutex m;
public:
    threadsafe_stack(){}
    threadsafe_stack (const threadsafe_stack& other)
    {
        std::lock_guard<<std::mutex> lock(other.m);

    ... rest of the code.

(in my version of the book this is listing 3.5)

Why I have direct access to other object private data (mutex m in this case)? Maybe I missed something or maybe this is a typo (I have Russian version of the book and there is no errata)

Thanks in advance.

Dmitry.

Upvotes: 0

Views: 767

Answers (1)

Fantastic Mr Fox
Fantastic Mr Fox

Reputation: 33854

This is perfectly normal, the private declaration only pertains to child classes and uses of this class, not to other instances of the same class. In fact this is how things like operator= work.

eg.

class A {
    private:
        int b;
    public:
         A() : b(rand()) {}
         A& operator=(const A& rhs) {
             b = rhs.b;
         }
};

class B : public A {
    public:
       void set(int newB) {
          b = newB; // Not ok.
       }
};

int main() {
    A a, aa;
    a.b = 5; // Not ok.

    a = aa; // Ok.
}

Upvotes: 1

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