using namespace std; and vectors

Question

I am working on a project for my c++ class and although my code looks fine to me (a beginner) whenever I run it I get error C2065 undeclared identifier in almost every line. I have done my research and have a feeling it has something to do with using namespace std; but I am not sure. Any help would be greatly appreciated.

The project is to create a vector that store a book list and then offer the user the ability to add a book to the list, display the list using an iterator, remove a book using an iterator, or store the data in an external file. Here is what I have so far:

#include <iostream>
#include <vector>
#include <string>
#include "bookColl.h"
#include <algorithm>
#include <fstream>

using namespace std;

int main()
{
    vector <string> bookCollection;
    string book1, book2, book3;

    cout << "Enter the first book in your book collection: " << endl;
    getline(cin, book1);

    cout << "\nEnter the second book in your book collection: " << endl;
    getline(cin, book2);

    cout << "\nEnter the third book in your book collection: " << endl;
    getline(cin, book3);

    bookCollection.push_back(book1);
    bookCollection.push_back(book2);
    bookCollection.push_back(book3);

    vector <string> ::iterator myITER;
    vector <string> ::const_iterator cITER;

    double decide;

    do
    {
        int choice = 0;
        cout << "What would you like to do?/n1.Add a book to your collection." <<
            "/n2.Display your book collection." << "/n3.Remove a book from your collection" << "/n4. Stop adding books and store the data in an external file" << "/nChoose a number 1 through 4: " << endl;

        if (choice == 1)
        {
            string addNew;
            addBook(&addNew);
            bookCollection.push_back(addNew);
        }

        else if (choice == 2)
        {
            cout << "Here are your books: " << endl;
            for (cITER = bookCollection.begin(); cITER != bookCollection.end(); cITER++)
            {
                cout << *cITER << endl;
            }
        }

        else if (choice == 3)
        {
            int removeBook;
            myITER = bookCollection.erase(bookCollection.begin() + removeBook);
            cout << "enter the numbered book position for the book you would like to remove: " <<
                "/n(The books in your book collection are labels for 0 up)" << endl;
            cin >> removeBook;
            cout << *myITER << endl;
        }

        else if (choice == 4)
        {
            sort(bookCollection.begin(), bookCollection.end());

            ofstream bookFile;
            bookFile.open("BookCollection.txt", ios::out | ios::app);
            bookFile << " This is a line of text. \n";
            bookFile << " This is a second line of text. \n";
            bookFile.close();
        }

        cout << "\nWould you like to run this program again? If so select 1 for Yes, and 0 for No" << endl;
        cin >> decide;

    } while (decide > 0);
}

bookColl.h

string addBook(string* pValOne);

bookColl.cpp

#include <iostream>
#include <vector>
#include <string>
#include "bookColl.h"

using namespace std;

string addBook(string* pValOne)
{
    string newBook;
    *pValOne = newBook;
    cout << "What is the name of the book you would like to add?" << endl;
    getline(cin, *pValOne);
    return newBook;
}

Answer 1

bookColl.h must look like this:

#ifndef BOOK_COLL_H
#define BOOK_COLL_H

#include <string>

std::string addBook(std::string* pValOne);

#endif

You need an include guard, and the full name of the class is std::string, not string; that's what you get with #include <string>. Your code does not compile because the using namespace std; comes after the #include "bookColl.h".

Speaking of using namespace, my advice would be to forget about it, at least for now. Just use std:: everywhere.

Answer 2

Avoid using namespace std; in header files like it was the plague. Read here for why.

After editing by Nathan, it is obvious that string isn't sufficient for your prototype. The compiler hasn't a clue what that type is, as std:string isn't made available as simply string until the subsequent using namespace std;. The solution is NOT to move the header include below using namespace std; rather you would never rely on using namespace std; or the .cpp file for header inclusion dependencies in the first place. In other words, That header is wrong to begin with. It should look something like this:

#ifndef MYAPP_BOOKCOLL_H
#define MYAPP_BOOKCOLL_H

#include <string>

std::string getBook();

#endif

Debate about #pragma once left out, and I refuse to participate in it. From there, your .cpp file can look like this:

#include "bookColl.h"
#include <iostream>
#include <string>

std::string getBook()
{
    std::string newBook;
    std::cout << "What is the name of the book you would like to add?" << std::endl;
    std::getline(std::cin, newBook);
    return newBook;
}

The inclusion of bookColl.h as the first header ensures your user-defined header file bookColl.h is properly implemented and has no reliance on the .cpp file including something the header itself relies on (and should therefore be including itself). It cannot (and should not) depend on the consuming .cpp file's previous declarations of system header includes.

I leave how to include bookColl.h in your main.cpp file and the slurry of errors in that file for you to address.