Unresolved External symbol

[jdougherty]

I need help with this error message please:

Error	1	error LNK2019: unresolved external symbol "public: __thiscall Book::Book(void)" (??0Book@@QAE@XZ) referenced in function _main	C:\Users\James\documents\visual studio 2013\Projects\Library Assistant\Library Assistant\Library.obj	Library Assistant

}

#include <iostream>
#include <fstream>
#include <iomanip>
#include "card.h"
#include "book.h"

using namespace std;

void CheckOut(Card c[], Book b[], int, int);
void ShowMenu();
int CreateCard(Card cards[], int numCards);
void PrintAllCards(Card cards[], int numCards);
void CheckIn(Card c[], Book b[], int, int);
void PrintAllBooks(Book books[], int numBooks);

int main()
{
	int numBooks = 0;
	int numCards = 0;
	int i = 0, j = 0;
	int command = 0;

	// declare an array of 20 cards
	Card cards[20];

	// declare an array of 20 books
	Book books[20];

	// declare a file pointer and open the cards file 
	ifstream cardInput("cards.txt");
	if (!cardInput)
	{
		cout << "File cards.txt could not be opened. Fatal error." << endl;
		exit(1);
	}

	cout << "File opened. Reading cards..." << endl;

	// read the next line from the file
	char Name[15];
	char junk[5];
	char phone[15];
	int CardID = 0;
	int temp = 0;

	cardInput.getline(Name, 13, ',');

	// tokenize the line to get the data for class variables

	while (cardInput)
	{
		cardInput.getline(Name, 13, ',');
		cardInput.getline(junk, 5, ',');
		cardInput.getline(phone, 12, ',');
		cardInput.getline(junk, 5, ',');
		cardInput >> CardID >> temp;

		Card working(Name, phone, CardID);
		cards[i] = working;
		i++;

	}
	cardInput.close();

	// declare a file pointer and open the books file 
	ifstream bookInput("books.txt");
	if (!bookInput)
	{
		cout << "File books.txt could not be opened. Fatal error." << endl;
		exit(1);
	}

	cout << "File opened. Reading books..." << endl;

	// read the next line from the file
	char Title[30];
	char Junk[5];
	char Author[30];
	int BookID = 0;
	int Temp = 0;

	bookInput.getline(Title, 13, ',');

	// tokenize the line to get the data for class variables
	
	while (bookInput)
	{
		bookInput.getline(Title, 30, ',');
		bookInput.getline(Junk, 5, ' ');
		bookInput.getline(Author, 10, ',');
		bookInput.getline(Junk, 5, ' ');

		bookInput >> BookID >> Temp;

		Book working(Title, Author, BookID);
		books[i] = working;
		i++;
	}
	bookInput.close();

	// display main menu
	ShowMenu();
	while (command != 0)
	{
		cin >> command;
		// execute the appropriate command
		switch (command){
		case 0:
			break;
		case 1:
			// call function to print all cards
			PrintAllCards(cards, numCards);
			break;
		case 2:
			// call functions to print all books
			PrintAllBooks(books, numBooks);
			break;
		case 3:
			// call to check out book
			CheckOut(cards, books, numCards, numBooks);
			break;
		case 4:
			// call to check in book
			CheckIn(cards, books, numCards, numBooks);
			break;
		case 5:
			// create new library cards
			numCards = CreateCard(cards, numCards);
			break;
		default:
			cout << "INVALID. Menu choices must be btween 0 and 5.";
		}

		ShowMenu();
	}
}

void ShowMenu()
{
	cout << " ------------------------------------- " << endl << endl;
	cout << "1. Show all Library Cards " << endl;
	cout << "2. Show all Books " << endl;
	cout << "3. Check out a Book " << endl;
	cout << "4. Check in a Book " << endl;
	cout << "5. Create a new Library Card " << endl;
	cout << "0. Exit the system " << endl << endl;
}

int CreateCard(Card cards[], int numCards)
{
	{

		char name[30];
		char phone[20];
		int cardID = 0;

		// add 1 to CardID to get ne CardID
		cout << "Enter the Card ID: ";
		cin >> cardID;

		// ask for name
		cout << "Enter your Name: ";
		cin >> name;

		// ask for phone number
		cout << "Enter your Phone Number: ";
		cin >> phone;

		// create a card
		Card temp(name, phone, cardID);

		// copy to arrau
		cards[numCards] = temp;
		numCards++;
		return numCards;
	}

}

void CheckOut(Card cards[], Book books[], int numBooks, int numCards)
{
	int c = 0, b = 0, nCard = 0, nBook = 0;

	cout << "Enter a card to search for: ";
	cin >> nCard;

	while (c < numCards && nCard != cards[c].getCardID())
	{
		c++;
	}
	
	if (c == numCards)
	{
		cout << "Card not Found! Create a new card and try again." << endl;
		return;
	}

	cout << "Card found for ";
	cards[c].printName();
	cout << "!" << endl;

	if (cards[c].getCardID() != 0)
	{
		cout << "HOWEVER... You have not returned your last book." << endl;
		return;
	}

	cout << "Enter the Book ID : ";
	cin >> nBook;

	while (b < numBooks && nBook != books[b].getBookID())
	{
		b++;
	}

	if (b == numBooks)
	{
		cout << "Book Not Found or Already Checked Out!" << endl;
		return;
	}
	
	if (books[b].getCardID() != 0)
	{
		cout << "Book Found! However... Someone has it checked out." << endl;
		return;
	}

	cards[c].setBookID(nBook);
	books[b].setCardID(nCard);

	cout << "Book Checked Out." << endl;
	cards[c].printName();
	
	cout << "has book ";
	books[b].getBookID();
	
	cout << " ";
	books[b].printTitle();
	cout << endl;
	
	return;
}

void CheckIn(Card c[], Book b[], int numBooks, int numCards)
{
	
}

void PrintAllCards(Card cards[], int numCards)
{
	int i = 0;

	for (i = 0; i < numCards; i++)
	{
		cards[i].print();
	}
}

void PrintAllBooks(Book books[], int numBooks)
{
	int j = 0;

	for (j = 0; j < numBooks; j++)
		books[j].print();
}

}

#include <iostream>
#include "book.h"

using namespace std;

Book::Book(char t[], char a[], int b)
{
	BookID = b;
	strcpy_s(Title, t);
	strcpy_s(Author, a);
	CheckedOut = false;
	CardID = 0;
}

int Book::getBookID()
{
	return BookID;
}

bool Book::isCheckedOut()
{
	return CheckedOut;
}

void Book::checkOut(int c)
{
	CardID = c;
	CheckedOut = false;
}

void Book::checkIn()
{
	CardID = 0;
	CheckedOut = false;
}

void Book::print()
{

}

void Book::printTitle()
{
	cout << Title;
}

void Book::setCardID(int c)
{

}

int Book::getCardID()
{
	return CardID;
}

}

#ifndef Book_H

#define Book_H


#include <iostream>
#include <iomanip>

class Book{

private:
	int BookID;
	char Title[30];
	char Author[30];
	bool CheckedOut;
	int CardID;

public:
	Book();
	Book(char t[], char a[], int b);
	int getBookID();
	void checkOut(int c);
	void checkIn();
	void print();
	void printTitle();
	bool isCheckedOut();
	int getCardID();
	void setCardID(int c);
};

#endif

}

Any help is appreciated.

[3hM2Nwbp]

A default constructor is declared for the Book class, but never defined. You can either explicitly define it or add the default keyword in its declaration.

[jdougherty]

Thanks for the reply. How would I go about doing that?

[tipaye]

You code has 2 constructors:

This one -

Declaration:
Book(char t[], char a[], int b);

Definition:

Book::Book(char t[], char a[], int b)
{
	BookID = b;
	strcpy_s(Title, t);
	strcpy_s(Author, a);
	CheckedOut = false;
	CardID = 0;
}

The other one is the default constructor -
Declaration:
Book();

But no definition. You should create a definition for it, it should take no arguments, and preferably initialise all the members to something sensible.

Example-

Definition:

Book()
{
        BookID = -1;
        ....
	CardID = -1; 
}

Try not use magic numbers (30) and prefer std::string to char [] in the first place.