Printing a text file which is stored line by line - c++

Question

I trying to write a function which searches for an ID and prints the book name and author name. I have been able to match the ID, however not able to properly print the book and author name. Text file is stored as such:
ID
book name
author name
Following is the code for my search function:
void searching() {
string search, id, name;
ifstream myfile("books.txt");
bool found = false;
string line;
cout << "\nEnter ID to search : ";
cin >> search;
int srchlen = search.length();
if(myfile.is_open()) {
while(getline(myfile, line)) {
id = line.substr(0, srchlen);
if(id == search) {
found = true;
break;
} else {
found = false;
}
}
if(found == true) {
name = line;
cout << "ID\tNAME\tAUTHOR\n";
cout << name;
} else {
cout << "ID doesnt exist";
}
}
}
Here is how the text file looks like (there is a blank line between each book):
98
crime and punishment
Dostoevsky
70
The Da Vinci Code
Dan Brown

Answer 1

So there's a logical flaw in your code that makes it harder to do what you want. The book data is stored on three separate lines, but your code reads one line at a time. Logically you should be reading three lines at a time. By doing this you'll have all the information available for one book at the same time.
Like this
string id, title, author;
while (getline(myfile, id) && getline(myfile, title) && getline(myfile, author)) {
string blank;
getline(myfile, blank); // skip the blank line between books
id = id.substr(0, srchlen);
if (id == search) {
found = true;
break;
} else {
found = false;
}
}
if (found == true) {
cout << "ID\tNAME\tAUTHOR\n";
cout << id << ' ' << title << ' ' << author << '\n';;
} else {
cout << "ID doesnt exist";
}
Note that reading the blank line is not part of the while condition. We don't want not to consider a book just because it wasn't followed by a blank line. This might happen at the end of the file for example.

Answer 2

To make it easier to deal with the data, I recommend putting the information about a book into a class (struct) and to add operators for reading/writing one book at a time from/to an istream/ostream.
#include <algorithm>
#include <fstream>
#include <iostream>
#include <limits>
#include <string>
struct Book {
std::string id;
std::string title;
std::string author;
};
// operator for reading one book title from any istream
std::istream& operator>>(std::istream& is, Book& b) {
std::getline(is, b.id);
std::getline(is, b.title);
std::getline(is, b.author);
// ignore the blank line between books in the file:
is.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
return is;
}
// operator for writing one book title to any ostream
std::ostream& operator<<(std::ostream& os, const Book& b) {
return os << b.id << '\n' << b.title << '\n' << b.author << "\n\n";
}
int main() {
std::string search;
std::cout << "\nEnter ID to search : ";
std::cin >> search;
if(std::ifstream myfile("books.txt"); myfile) {
Book book;
// read one book at a time from the stream using the added
// operator>>
while(myfile >> book) {
if(book.id == search) {
// book found, write it to cout using the added
// operator<<
std::cout << book;
break;
}
}
}
}

Answer 3

By taking some advantages of C++ such as vector, you can make the code easier:
#include <iostream>
#include <vector>
#include <fstream>
const char *fileName = "books.txt";
// structure of the file
struct book {
int ID;
std::string author;
std::string bookName;
};
int main(void) {
std::ifstream file(fileName); // to read the file
std::vector<book> vec; // to find the content required
int ID; // the ID to find
book temp; // temporary 'book' to insert in vector
bool found = false;
// if the file was unable to open
if (!file.is_open()) {
std::cout << "Unable to open the file." << std::endl;
return -1;
}
// getting the content of the file
while (file >> temp.ID >> temp.bookName >> temp.author)
vec.push_back(temp);
std::cout << "Enter the ID to find: ";
std::cin >> ID;
// matching the IDs
for (size_t i = 0, len = vec.size(); i < len; i++)
// prints when ID asked to show is present in the file
if (vec[i].ID == ID) {
std::cout << "ID: " << vec[i].ID << " | Author: "
<< vec[i].author << " | Name: " << vec[i].bookName;
found = true;
break;
}
if (!found)
std::cout << "The ID does not exist." << std::endl;
return 0;
}
Supposing the books.txt contains:
// FORMAT: ID _ Book _ Author
10 BookABC John
20 BookXYZ Ben
30 CodingBook Rock
Then the output would be something like:
Enter the ID to find: 30
ID: 30 | Author: Rock | Name: CodingBook