Constructor

Question

Hi.
How to complete the declaration of these following class, such that the class can keep track of how many objects have been instantiated since the beginning of a program that uses it? :

//answers on the wide blank spaces

class Book {
public:

const char * getTitle() const
{
return m_title;
}
void setTitle(const char * t)
{
strcpy(m_title, t)
}

private:
char m_title[256];

};

Answer 1

Use a static member that is to be incremented by one every time when the constructor is called. That is local to a class instead of a single instance, and will be updated whenever a new object calls the Constructor.

Eg :

class Book
{
static int book_ct;
char m_title[256];
public :
Book() { book_ct++; }
// More code...
};
int Book::book_ct=0;

To check its value after some operation, you will have to use a static member, like :

static void print_count()
{ cout<<book_ct<<" Books Exist\n"; }

And then you call it in main like this :

int main()
{
Book books[5];
Book::print_count();
// More code follows...
}

Answer 2

thank you