当后代需要不同的参数列表时，应如何在基类中定义抽象方法？

Question

Here is my code:

class LibItem
{
public:
    virtual void PrintDetails() = 0;
    virtual void setDetails() = 0;
    void setTitle(string TitleName)
    {
        Title = TitleName;
    }
    string getTitle()
    {
        return Title;
    }
    void setReleaseDate(string date)
    {
        ReleaseDate = date;
    }
    string getReleaseDate()
    {
        return ReleaseDate;
    }
    void setAuthor(string AuthorName)
    {
        Author = AuthorName;
    }
    string getAuthor()
    {
        return Author;
    }
    void setCopyright(string CopyrightDetails)
    {
        Copyright = CopyrightDetails;
    }
    string getCopyright()
    {
        return Copyright;
    }
    void setGenre(string GenreDetails)
    {
        Genre = GenreDetails;
    }
    string getGenre()
    {
        return Genre;
    }
    void setStatus(string StatusDetails)
    {
        Status = StatusDetails;
    }
    string getStatus()
    {
        return Status;
    }
private:
    string Title;
    string ReleaseDate;
    string Author;
    string Copyright;
    string Genre;
    string Status;
};

class Book : public LibItem
{
public:
    Book(string TitleName)
    {
        setTitle(TitleName);
    }
    void setISBN(int ISBNDetails)
    {
        ISBN = ISBNDetails;
    }
    int getISBN()
    {
        return ISBN;
    }
    void setDetails(string setBookTitle, string setBookAuthor, string setBookReleaseDate, string setBookCopyright, string setBookGenre, string setBookStatus, int setBookISBN)
    {
        setTitle(setBookTitle);
        setAuthor(setBookAuthor);
        setReleaseDate(setBookReleaseDate);
        setCopyright(setBookCopyright);
        setGenre(setBookGenre);
        setStatus(setBookStatus);
        setISBN(setBookISBN);
    }
    void PrintDetails()
    {
        cout << "Title: " << getTitle() << endl;
        cout << "Author: " << getAuthor() << endl;
        cout << "Release Date: " << getReleaseDate() << endl;
        cout << "Copyrite: " << getCopyright() << endl;
        cout << "Genre: " << getGenre() << endl;
        cout << "Status: " << getStatus() << endl;
        cout << "ISBN: " << getISBN() << endl;
    }

private:
    Book();
    int ISBN;

};

class DVD : public LibItem
{
public:
    DVD(string TitleName)
    {
        setTitle(TitleName);
    }
    void setRunningTime(int RunningTimeDetails)
    {
        RunningTime = RunningTimeDetails;
    }
    int getRunningTime()
    {
        return RunningTime;
    }
    void setDirector(string DirectorDetails)
    {
        Director = DirectorDetails;
    }
    string getDirector()
    {
        return Director;
    }
    void setStudio(string StudioDetails)
    {
        Studio = StudioDetails;
    }
    string getStudio()
    {
        return Studio;
    }
    void setProducer(string ProducerDetails)
    {
        Producer = ProducerDetails;
    }
    string getProducer()
    {
        return Producer;
    }
    void setDetails(string setDVDTitle, string setDVDAuthor, string setDVDReleaseDate, string setDVDCopyright, string setDVDGenre, string setDVDStatus, int setDVDRunningTime, string setDVDDirector, string setDVDStudio, string setDVDProducer)
    {
        setTitle(setDVDTitle);
        setAuthor(setDVDAuthor);
        setReleaseDate(setDVDReleaseDate);
        setCopyright(setDVDCopyright);
        setGenre(setDVDGenre);
        setStatus(setDVDStatus);
        setDirector(setDVDDirector);
        setStudio(setDVDStudio);
        setProducer(setDVDProducer);
    }
    void PrintDetails()
    {
        cout << "Title: " << getTitle() << endl;
        cout << "Author: " << getAuthor() << endl;
        cout << "Release Date: " << getReleaseDate() << endl;
        cout << "Copyrite: " << getCopyright() << endl;
        cout << "Genre: " << getGenre() << endl;
        cout << "Status: " << getStatus() << endl;
        cout << "Running Time: " << getRunningTime() << endl;
        cout << "Director: " << getDirector() << endl;
        cout << "Studio: " << getStudio() << endl;
        cout << "Producer: " << getProducer() << endl;
    }

private:
    DVD();
    int RunningTime;
    string Director;
    string Studio;
    string Producer;

};

I am having trouble with the virtual void setDetails();

I am wanting both the Book and DVD class to have a method called setDetails to set the details. The problem is, both the Book class and the DVD class have different arguments for this method.

How can I achieve this?

How is the best way to solve this problem?

Answer 1

Since

setDetails(string setDVDTitle, string setDVDAuthor, string setDVDReleaseDate, string setDVDCopyright, string setDVDGenre, string setDVDStatus, int setDVDRunningTime, string setDVDDirector, string setDVDStudio, string setDVDProducer)

only makes sense for a DVD object, and

setDetails(string setBookTitle, string setBookAuthor, string setBookReleaseDate, string setBookCopyright, string setBookGenre, string setBookStatus, int setBookISBN)

only makes sense for a Book, the methods shouldn't be virtual , nor in the base class.

Say I give you a LibItem* and I tell you to set its details. What do you do? Does it make sense to set its details, since they differ from one concrete implementing class to another?

The base class should only have the method that sets:

string Title;
string ReleaseDate;
string Author;
string Copyright;
string Genre;
string Status;

which shouldn't be virtual , since its behavior doesn't change from implementation to implementation, and you should set specific details on the implementing classes themselves.

Answer 2

The abstract base class can only contain functions that are common to all derived classes, so if you need different functions in different derived classes, they can't go in the base class.

You could downcast to get the derived type, and access its type-specific functions:

LibItem & item = some_item();

if (Book * book = dynamic_cast<Book*>(&item)) {
    book->setDetails(book_details);
} else if (DVD * dvd = dynamic_cast<DVD*>(&item)) {
    dvd->setDetails(dvd_details);
}

If you have many different types, and many type-specific operations, then it might be worth considering the Visitor pattern ; but that's overkill in most situations.

Answer 3

you cant, you need common interface. http://www.tutorialspoint.com/cplusplus/cpp_interfaces.htm . This article will help you a lot in understanding of abstract classes. Member function which has different arguments for different childs shouldnt be virtual.

Looking into your code:

try to change your arguments type from "string" to "const string&" you will avoid copies.

Answer 4

virtual void LibItem::setDetails() = 0;

and

void Book::setDetails(string setBookTitle, string setBookAuthor, string setBookReleaseDate, string setBookCopyright, string setBookGenre, string setBookStatus, int setBookISBN)

and

void DVD::setDetails(string setDVDTitle, string setDVDAuthor, string setDVDReleaseDate, string setDVDCopyright, string setDVDGenre, string setDVDStatus, int setDVDRunningTime, string setDVDDirector, string setDVDStudio, string setDVDProducer)

are different methods, so, there is no overloading in your code.

BTW. Don't forget about virtual destructor in your LibItem...

Answer 5

There are two ways you could handle this. The first involves varargs, declaring the interface in the base to be setDetails( std::string const& title... ) . I will not go further into this way, however, as it is a sure path to unexplained crashes later down the road. The other solution is to use something like: setDetails( std::map< std::string, std::string > const& ) , and in the concrete implementation extract the details you want by name. Even then, I'm not sure it's a good solution, since given a LibItem* , you don't know what to put in the map. (It could be a valid solution if you get the type of object and the list of details from the user. Even then, I'd probably encapsulate this into a factory function, which would know the type it is creating, verify that the details correspond, and then pass all of the details to the constructor.)

And while I'm at it: you can't use an int for ISBN. The most reasonable representation is a string.