c++ adding subclass to array of base class?

Question

i have a class book and 2 subclass lerningbook,readingbook and i am trying to create a list of books book* listofbooks and add to it the subclass

Book* listOfBooks;

void Mang::addBookToList(Book b3)
{
    Book* temp;
    temp=listOfBooks;
    lobsize++;
    listOfBooks=new Book[lobsize];
    int i;
    for(;i<lobsize;i++)
    {
        listOfBooks[i]=temp[i];
    }
    listOfBooks[i]=b3;
}

problem is when i am trying to send it the subclass this not accpecting it i tryed to use template so the function will be able to take any class but it didnt help
the error am geting is:
no suitable user defined conversion from lerningbook to book exsists
guessing i need to implement same type of function that will allow me to do this but i dont know wich one hope one of you can help me out thx in adv :)
(i know i am missing the delete[] on the temp array sort of got stuck on this problem)

Community · Accepted Answer · 2017-05-23 12:20:05Z

1

b3 is a Book, but listoOfBooks is an array of Book*. You need to pass a Book* to addBookToList, not just for the assigment but to avoid object slicing.

If this is not a learning exercise, use a std::vector<Book*> instead or a std::vector<std::shared_ptr<Book>>. The std::vector will dynamically grow as required and the use of a smart pointer will automatically delete the elements when the vector is destroyed.

If you choose use of the Book* ensure you obey the What is The Rule of Three?. This could just be making Mang non-copyable by declaring the copy constructor and assignment operator private.

Note that i is uninitialised in for loop and the following assignment is out of bounds access on the array as i == lobsize after the for:

listOfBooks[i]=b3;

array indexes run from 0, so lobsize - 1 is the index of the last element.

edited May 23, 2017 at 12:20

CommunityBot

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answered Jun 26, 2012 at 21:55

hmjd

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