Getline equivalent for class and int, and also 'no viable overloaded =' error

Question

class Book{
public:
string _title;
string _author;
string _publisher;
Date _published;
float _price;
string _isbn;
int _page;
int _copies;


Book(void);
Book(string, string, string, Date, float, string, int, int);
};

Book::Book(void)
{
 _title = "";
 _author = "";
 _publisher = "";
 _published = 0;
 _price = 0;
 _isbn = "";
 _page = 0;
 _copies = 0;

Where Date is a class including ints for day, month, and year. This generates a no viable overloaded = error.

int main(void)
{
LinkedList myList;
ifstream myFile("sample.txt");

string title;
string author;
string publisher;
Date published;
float price;
string isbn;
int page;
int copies;


while( myFile )
{
getline(myFile,title);
getline(myFile,author);
getline(myFile,publisher);
getline(myFile,published);
getline(myFile,price);
getline(myFile,isbn);
getline(myFile,page);
getline(myFile,copies);

myList.insert_rear(new    Book(title,author,publisher,published,price,isbn,page,copies));
}

myList.print_list();

return 0;

}

For getline published(Date class), price(int), page(int), and copies(int) I'm getting a no matching function call for getline. I know getline is for strings so I expected that error. What can I do instead?

Thank you, and if you need to see more code let me know.

Answer 1

One cannot simply std::getline into an int. Seriously. It's harder than walking into Mordor.

A few ways to do this.

One is to intermix std::getline and use of the >> operator. But

myFile >> price;
getline(myFile,isbn);

Won't work because myFile >> price; leaves the end of line in the stream to be gobbled up by getline(myFile,isbn) resulting in an empty string in isbn. Something simple like

char end_of_line;
myFile >> price >> end_of_line;
getline(myFile,isbn);

will do the job, assuming your file strictly adheres to the format.

myFile >> price;
myFile.ignore(numeric_limits<streamsize>::max(), '\n');
getline(myFile,isbn);

is safer. It discards everything up to and including the end of the line.

Sadly you can't do this with published unless you've written an operator>> for Date.

The next good option is to read in everything as a string and then convert it to the appropriate datatype before calling the Book constructor. Something along the lines of

int main()
{
    ifstream myFile("sample.txt");

    string title;
    string author;
    string publisher;
    string published;
    string price;
    string isbn;
    string page;
    string copies;

    while (getline(myFile, title) &&
           getline(myFile, author) &&
           getline(myFile, publisher) &&
           getline(myFile, published) &&
           getline(myFile, price) &&
           getline(myFile, isbn) &&
           getline(myFile, page) &&
           getline(myFile, copies))
    {
        myList.insert_rear(new Book(title,
                                    author,
                                    publisher,
                                    string_to_date(published), // function does not exist 
                                    stof(price),
                                    isbn,
                                    stoi(page),
                                    stoi(copies)));
    }

    return 0;
}

Off topic: Note how all of the getlines are in the while this will not enter the body of the loop unless reading of all of the inputs succeeded.

while( myFile )

tests for goodness at the beginning before all of the values are read. All this tells you is the last thing you read was good. It give no guarantees about the quality of the next things you will read. Currently getline(myFile,title); could fail along with everything after it and you'll build the new Book with the results of invalid reads. Always read, test that you read good information, and only then use what you read.

Probably the best way is to take either of the above two methods and build them into an operator>> for Book.

Then you can

int main()
{
    ifstream myFile("sample.txt");

    Book temp;
    while (myFile >> temp)
    {
        myList.insert_rear(new Book(temp));
    }

    return 0;
}

This even makes it easy to get rid of the dynmaically allocated Book, and that's worth it's weight in gold.