C++ inheritance, add member to a derived class and redefine constructor

Question

I've a noob problem with C++.

I've a class Book:

class Book {
public:
    string name;
    Author author;
    double price;
    int qtyInStock;

public:
    Book(const string & name, 
         const Author & author, 
         double price, 
         int qtyInStock = 0);
    string getName() const;
    Author getAuthor() const;
    double getPrice() const;
    void setPrice(double price);
    int getQtyInStock() const;
    void setQtyInStock(int qtyInStock);
    void print() const;
    string getAuthorName() const;
};

with the constructor:

Book::Book(
    const string & name, 
    const Author & author, 
    double price, 
    int qtyInStock)
: name(name), author(author) 
{ // Init object reference in member initializer list
    // Call setters to validate price and qtyInStock
    setPrice(price);
    setQtyInStock(qtyInStock);
}

Now i wanto to create a new class that derive from it "BookDigital",written below:

class DigitalBook:public Book
{
public:
    string site;
    DigitalBook(const string & name, 
                const Author & author, 
                double price, 
                int qtyInStock = 0,
                string & site);
};

With Constructor:

DigitalBook:DigitalBook(
    const string & name, 
    const Author & author, 
    double price, int qtyInStock,
    string & site)
: name(name), author(author) { // Init object reference in member initializer list
    // Call setters to validate price and qtyInStock
    setPrice(price);
    setQtyInStock(qtyInStock);
}

I've add a member "site" for a digital book

When I compile this, it shows the message error:

||=== Build: Debug in Test C++ (compiler: GNU GCC Compiler) ===|
C:\Users\aalovisi\Desktop\Test C++\Book.h|34|error: default argument missing for parameter 5 of 'DigitalBook::DigitalBook(const string&, const Author&, double, int, std::string&)'|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp|14|error: found ':' in nested-name-specifier, expected '::'|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp||In constructor 'DigitalBook::DigitalBook(const string&, const Author&, double, int, std::string&)':|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp|15|error: class 'DigitalBook' does not have any field named 'name'|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp|15|error: class 'DigitalBook' does not have any field named 'author'|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp|15|error: no matching function for call to 'Book::Book()'|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp|15|note: candidates are:|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp|7|note: Book::Book(const string&, const Author&, double, int)|
C:\Users\aalovisi\Desktop\Test C++\Book.cpp|7|note:   candidate expects 4 arguments, 0 provided|
C:\Users\aalovisi\Desktop\Test C++\Book.h|8|note: Book::Book(const Book&)|
C:\Users\aalovisi\Desktop\Test C++\Book.h|8|note:   candidate expects 1 argument, 0 provided|
||=== Build failed: 5 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

Why?Thank you for help

Answer 1

If a function has default value for some parameter then all other parameters that go further should have default value too. This is what the compiler is trying to tell you in its first message.

Answer 2

I think your problem is you define a default value for the forth parameter in constructor (int qtyInStock = 0) but not for the fifth one (string & site).

You should either avoid the defalut for parameter 4 or give a default for parameter 5.

Also I think you have problems in your constructors: DigitalBook::DigitalBook should call the base class constructor, I guess

Answer 3

Buidling a DigitalBook object means a Book object has to be built. However you don't have a defaut constructor for Book (with no argument)

Therefore when trying to create your DigitalBook the father class cannot be built and you get an error.

What you should do is

DigitalBook:DigitalBook(const string & name,
                        const Author & author,
                        double price,
                        int qtyInStock,
                        string & _site) :
     Book(name, author, price, qtyInStock),
     site(_site)
{
}

That way you specify in your derivated class's constructor how to build the inherent class's object it relies on

Answer 4

default argument missing for parameter 5

You have a default argument for the fourth parameter, but not the fifth. If one parameter has a default argument, then so must all the ones following it. Either make qtyInStock the last parameter, remove its default argument, or give a default argument to site.

found ':' in nested-name-specifier, expected '::'

You wrote DigitalBook:DigitalBook instead of DigitalBook::DigitalBook.

class 'DigitalBook' does not have any field named 'name'
class 'DigitalBook' does not have any field named 'author'

You can only initialise members of the current class, not a base class, in the constructor's initialiser list. Instead of trying to initialise each base member, initialise the whole base subobject:

DigitalBook::DigitalBook(const string & name, const Author & author, double price, int qtyInStock, string & site)
    : Book(name, author, price, qtyInStock), site(site)
{}

There's no need to call setPrice and setQtyInStock, assuming the Book constructor does the right thing with those arguments.

no matching function for call to 'Book::Book()'

That's because, since you didn't include an entry for Book in the initialiser list, it needed to be default-initialised; but it doesn't have a suitable constructor. Adding the initialiser as described above will also fix this.

Answer 5

Resolved with this one, Thank You :)

class Person
{
public:
std::string m_strName;
int m_nAge;
bool m_bIsMale;

std::string GetName() { return m_strName; }
int GetAge() { return m_nAge; }
bool IsMale() { return m_bIsMale; }
void print() const;

Person(std::string strName = "", int nAge = 0, bool bIsMale = false)
    : m_strName(strName), m_nAge(nAge), m_bIsMale(bIsMale)
{
}
};

class BaseballPlayer : public Person
{
public:
double m_dBattingAverage;
int m_nHomeRuns;

BaseballPlayer(double dBattingAverage = 0.0, int nHomeRuns = 0)
   : m_dBattingAverage(dBattingAverage), m_nHomeRuns(nHomeRuns)
{
}
};