错误：无法访问成员

Question

I have these two classes:

class Hand
{
public:
    int getTotal();
    std::vector<Card>& getCards();
    void add(Card& card);
    void clear();
private:
    std::vector<Card> cards;
};

class Deck : public Hand
{
public:
    void rePopulate();
    void shuffle();
    void deal(Hand& hand);
};

Where the shuffle() function is declared as follows:

void Deck::shuffle()
{
    std::random_shuffle(cards.begin(), cards.end());
}

However, this returns the following error:

'Hand::cards' : cannot access private member declared in class 'Hand'

Should I just include a function such as std::vector<Card>& getCards() or is there another way to avoid the error.

Answer 1

You can declare cards as protected :

class Hand
{
public:
    int getTotal();
    std::vector<Card>& getCards();
    void add(Card& card);
    void clear();
protected:
    std::vector<Card> cards;
};

class Deck : public Hand
{
public:
    void rePopulate();
    void shuffle();
    void deal(Hand& hand);
};

Answer 2

Since your class Deck inherits from Hand (and it is not a friend class nor is the method Deck::shuffle() ), you could simply make cards protected instead of private . This ensures the encapsulation is in place but the method is accessible by all derivative classes.

Just take a look, among other references and tutorials, there:

1. http://www.cplusplus.com/doc/tutorial/inheritance/
2. http://www.learncpp.com/cpp-tutorial/115-inheritance-and-access-specifiers/

Answer 3

In case of inheritance (your case) the best solution is to make cards protected:

protected:
    std::vector<Card> cards;

But in general you can make them friends.

class Hand
{
friend class Deck;
public:
    int getTotal();
    std::vector<Card>& getCards();
    void add(Card& card);
    void clear();
private:
    std::vector<Card> cards;
};