Thread: Long question about Class and output

Hello,

I'm currently working on a program where I have a file I retrieve data from, and sort the different options (title, author, genre) and display the sorted list for each option. I have to make a header file for the class, and a main file that utilizes the header. I'm currently stuck because I am not seeing any output on my screen besides asking the user to enter a choice + entering a choice. The resulting sorted list does not show up but I'm not sure where in my header file I am making a mistake.

Example of a line in the input file is
"Title of book, author, genre"

Code:

#ifndef COLLECTION_H#define COLLECTION_H
#include <iostream>
#include <vector>
#include <fstream>
#include <sstream>
#include <algorithm>


using namespace std;


class Collection
{
    private:
        struct Book
        {
            string title;
            string author;
            string genre;
        };
        vector<Book> books;


    public:
	
	Collection()
	{
		ifstream inFile;
		Book book;
		string line;
		
		inFile.open("Books.txt");
		
		while(inFile.fail())
		cout << "File not found.";
		
		while(inFile.eof())
		{
			getline(inFile, line);
			stringstream stream(line);
			getline(stream, book.title, ',');
			getline(stream, book.author, ',');
			getline(stream, book.genre, '\n');
			books.push_back(book);
		}				
	}   
 
    void sortByTitle()
    {
        sort(books.begin(), books.end(), [](Book b1, Book b2) { return b1.title < b2.title; });
    }
    
    void sortByAuthor()
    {
        sort(books.begin(), books.end(), [](Book b1, Book b2) { return b1.author < b2.author; });
    }
    
    void sortByGenre()
    {
        sort(books.begin(), books.end(), [](Book b1, Book b2) { return b1.genre < b2.genre; });
    }
    
    void output()
    {
    	for (auto val:books )
    	{
    		cout << val.title << endl;
    		cout << val.author << endl;
    		cout << val.genre << endl;
		}
	}
};


#endif

Code:

#include <iostream>#include "Collection.h"
using namespace std;


int main() 
{
	Collection collect;
	int choice;
	
	cout << "Please enter a number to sort the books by the following options:\n";
	cout << "\tEnter 1 to sort by Title\n";
	cout << "\tEnter 2 to sort by Author\n";
	cout << "\tEnter 3 to sort by Genre\n";
	cin >> choice;
	
	if (choice == 1)
	{
		collect.sortByTitle();
	}
	
	if (choice == 2)
	{
		collect.sortByAuthor();
	}
	
	if (choice == 3)
	{
		collect.sortByGenre();
	}
	
	collect.output();
}

Originally Posted by laserlight

Well, you can still define the I/O for the Book struct. A struct nested within a class is still a class, but within that outer class' scope and with the access defaults of a struct.

For the Collection constructor, it should take an open ostream argument. If you want to open the file in the constructor, then what do you do if it fails? At the moment you're printing an error message (incorrectly in a loop), and then proceeding to read from the unopen file anyway. The right approach is to throw an exception, but the easier approach is to handle the opening of the file before creating the Collection object.

Code:

while (getline(inFile, line))

Thanks laserlight. Using a while loop for getline works much better and cleaner than the other approach I was using. It is a shame that I am being taught bad code in my C++ class when there is much more efficient ways of doing it.

This essentially fixed my whole problem. Thanks again!

Soooo I spoke too soon. For some reason I'm getting some weird output when I run my program. Mainly theres seems to be random duplicates appearing and I'm not too sure why.
My current code:

Code:

#ifndef COLLECTION_H
#define COLLECTION_H
#include <iostream>
#include <fstream>
#include <vector>
#include <sstream>
#include <algorithm>
#include <string>
#include <iomanip>


using namespace std;


class Collection
{
    private:
        struct Book
        {
            string title;
            string author;
            string genre;
        };
        vector<Book> books;


    public:   
 	
 		Collection()
 		{
 			Book book;
 			ifstream inFile;
 			string filename, text;
 			
 			inFile.open("Books.txt");
 			if (inFile.fail())
 			{
 				cout << "File not found. Please enter file name: ";
 				cin >> filename;
 				inFile.open(filename);
			}
			
			while (getline(inFile,text))
			{
				stringstream lineStream(text);
				getline(lineStream, book.title, ',');
				getline(lineStream, book.author, ',');
				getline(lineStream, book.genre);
				books.push_back(book);					
			}


			inFile.close();
		}


   	void sortByTitle()
    	{
        	sort(books.begin(), books.end(), [](Book b1, Book b2) { return b1.title < b2.title; });
    	}
    	
   	void sortByAuthor()
    	{
        	sort(books.begin(), books.end(), [](Book b1, Book b2) { return b1.author < b2.author; });
    	}
    	
    	void sortByGenre()
    	{
        	sort(books.begin(), books.end(), [](Book b1, Book b2) { return b1.genre < b2.genre; });
    	}
    	
    	void output()
    	{
    		cout << left << setw(41) << "Title" << left << setw(25) << "Author" << setw(20) << "Genre\n";


    		for (auto val:books)
    		{
    			cout << left << setw(40) << val.title << left << setw(25) << val.author << setw(20) << val.genre << endl;
			}
		}
};
#endif

This is the output I get when I put in sort by title. It sorts the titles correctly however there are a bunch of duplicate outputs prior to the correct sorted file. It is different when sorting by author & genre but the error in code must be the same for all sorting options.

Code:

There are 3 fields for each book: title, author and genre.
Please select an option to sort the books by a particular field by entering the correct number.
1 = Sort by title
2 = Sort by author
3 = Sort by genre
Please enter a sorting option: 1
Title                                    Author                   Genre
                                                       Tony Gaddis              technical
                                         Liu Cixin                science fiction
                                         Kenzo Kitakana           fiction
                                         Gabriel Garcia Marquez   fiction
                                         Carol Dweck              psychology
                                         Ken Follet               historical fiction
                                         Ken Follett              historical fiction
                                         Bjarne Stroustrup        technical
                                         Elmarsi & Navathe        technical
Ashes                                    Kenzo Kitakana           fiction
Fall of Giants                           Ken Follet               historical fiction
Fundamentals of Database Systems         Elmarsi & Navathe        technical
Mindset: The New Psychology of Success   Carol Dweck              psychology
One Hundred Years of Solitude            Gabriel Garcia Marquez   fiction
Replay                                   Ken Grimwood             fantasy
Starting out with c++                    Tony Gaddis              technical
The C++ Programming Language             Bjarne Stroustrup        technical
The Dark Forest                          Liu Cixin                science fiction
The Pillars of the Earth                 Ken Follett              historical fiction

Not exactly sure why this is happenig. There are no white spaces in my input file but it seems to be picking up random lines due to something?

This is simply it

This is my train of thought

Code:

while (getline(inFile,text))

Tells me that as long as the program can read a line of string it'll do the following

Code:

 
{
    stringstream lineStream(text);
    getline(lineStream, book.title, ',');
    getline(lineStream, book.author, ',');
    getline(lineStream, book.genre);
    books.push_back(book);                    
}

I associate each individual string object within text string which essentially allows me to get title, author, and genre. Then I push each of those string values into the vector books. This continues for as long as the program can perform getline from the input file, inFile. I have no clue where it is pulling the other garbage from. From my logical pov; it's behaving in a way I don't see how it is. I guess I'm missing the logic or my train of thought is incorrect

Originally Posted by laserlight

Your logic sounds correct, but you're not doing sufficient error checking, e.g., you assume that the line is non-empty and that the getline calls succeed.

Maybe it is a newline sequence problem, but either way, stop pontificating about your logic and debug your program. You have to know what's going on before you can proceed to find out if the error is with your logic or your implementation.

Makes sense. I guess for it is hard to debug my program when I can't think of potential errors. I am assuming there are no blank lines because looking at my text file there simply isn't any.

I implemented a quick if condition to skip any blanks

Code:

			while (getline(inFile,text))
			{
				if (text == "")
				continue;
				stringstream lineStream(text);
				getline(lineStream, book.title, ',');
				getline(lineStream, book.author, ',');
				getline(lineStream, book.genre);
				books.push_back(book);					
			}

It has worked and all my duplicates I was seeing before are not showing up now. Now that it has been debugged essentially, I can't figure out what the problem was. Since I am essentially cheating by knowing what my input file looks exactly like. I don't see anywhere in the text file that has blank lines between my string lines that could have been causing my error. But obviously, the program is telling me different by adding in that command and that there were blank lines to skip. Is there just something inherent about my text file that I am not seeing visually?

Originally Posted by laserlight

Are you programming on Windows? It looks like it from the image you posted.

Yes I am programming in Windows 10 using Dev-C++