How to work with file handling in C++

Prerequisite: File Handling through C++ Classes

In C++, files are mainly dealt by using three classes fstream, ifstream, ofstream available in fstream header file. In this post we will discuss how to store data using file handling.

The idea is to take an example of Book Database and implement it the same in C++. Below are the functionality used:

• How to Insert book record
• How to view all book record
• How to search book record
• How to delete book record
• How to update book record

Below is the implementation of file handling operations:

C++

// C++ program for implementing the above
// mentioned functionalities
#include <bits/stdc++.h>
#include <conio.h>
#include <fstream>
using namespace std;

// Book class
class Book {
private:
    int bookid;

    // Max book title size 20
    char title[20];
    float price;

public:
    // Default Constructor
    Book()
    {
        bookid = 0;
        strcpy(title, "no title");
        price = 0;
    }

    // Function for taking book data
    void getBookData()
    {
        cout << "Enter bookid, title, "
             << " price: ";
        cin >> bookid;
        cin.ignore();
        cin.getline(title, 19);
        cin >> price;
    }

    // Function for showing book data
    void showBookData()
    {
        cout << "\n"
             << bookid
             << " " << title << " " << price;
    }

    int storeBook();
    void viewAllBooks();
    void searchBook(char*);
    void deleteBook(char*);
    void updateBook(char*);
};

// Function for update book data
void Book::updateBook(char* t)
{
    fstream file;

    // Open the file
    file.open("myfile3.txt",
              ios::in | ios::out | ios::ate | ios::binary);
    file.seekg(0);
    file.read((char*)this, sizeof(*this));

    // Read the file
    while (!file.eof()) {
        if (!strcmp(t, title)) {
            getBookData();

            file.seekp(file.tellp() - sizeof(*this));
            file.write((char*)this, sizeof(*this));
        }
        file.read((char*)this, sizeof(*this));
    }

    // Close the file
    file.close();
}

// Function for delete book data
void Book::deleteBook(char* t)
{
    ifstream fin;
    ofstream fout;
    fin.open("myfile3.txt",
             ios::app | ios::binary);
    if (!fin)
        cout << "\n File not found";
    else {
        fout.open("tempfile.txt",
                  ios::app | ios::binary);
        fin.read((char*)this, sizeof(*this));

        // Until end of file is not reached
        while (!fin.eof()) {
            if (strcmp(title, t))
                fout.write((char*)this, sizeof(*this));
            fin.read((char*)this, sizeof(*this));
        }
        fin.close();
        fout.close();
        remove("myfile3.txt");
        rename("tempfile.txt", "myfile3.txt");
    }
}

// Function to search the Book
void Book::searchBook(char* t)
{
    int counter = 0;
    ifstream fin;
    fin.open("myfile3.txt",
             ios::in | ios::binary);

    // If file is not found
    if (!fin)
        cout << "File not found";
    else {
        fin.read((char*)this, sizeof(*this));

        // Until end of file is not reached
        while (!fin.eof()) {
            if (!strcmp(t, title)) {
                showBookData();
                counter++;
            }
            fin.read((char*)this, sizeof(*this));
        }
        if (counter == 0)
            cout << "No record found";
        fin.close();
    }
}

// Function to view all the Book
void Book::viewAllBooks()
{
    ifstream fin;

    // Open function open file named
    // myfile.txt
    fin.open("myfile3.txt", ios::in | ios::binary);
    if (!fin)
        cout << "File not found";

    else {
        fin.read((char*)this, sizeof(*this));

        // Until end of file is
        // not reached
        while (!fin.eof()) {
            showBookData();

            // read is object of ifstream
            // class which is used for
            // read data of file
            fin.read((char*)this, sizeof(*this));
        }
        fin.close();
    }
}

// Function to implement the store of
// all the books
int Book::storeBook()
{
    if (bookid == 0 && price == 0) {
        cout << "book data not"
             << " initialized";
        return (0);
    }
    else {
        ofstream fout;

        // In the below line open function
        // used to open files. If the file
        // does not exist then it will
        // create the file "myfile.txt"
        fout.open("myfile3.txt", ios::app | ios::binary);

        // Write function is used for
        // data to write in the file
        fout.write((char*)this, sizeof(*this));
        fout.close();
        return (1);
    }
}

// Function to display the menu of the
// current menu-driver
int menu()
{
    int choice;
    cout << "\nBook Management";
    cout << "\n1.Insert book record";
    cout << "\n2.View all book record";
    cout << "\n3.Search book record";
    cout << "\n4.Delete book record";
    cout << "\n5.Update book record";
    cout << "\n6.Exit";
    cout << "\n\nEnter your choice : ";
    cin >> (choice);
    return (choice);
}

// Driver Code
int main()
{

    // Object of the class Book
    Book b1;
    char title[20];

    while (1) {
        system("cls");
        switch (menu()) {
        case 1:
            b1.getBookData();
            b1.storeBook();
            cout << "\nRecord inserted";
            break;

        case 2:
            b1.viewAllBooks();
            break;

        case 3:
            cout << "\nEnter title of "
                 << "book to search : ";
            cin.ignore();
            cin.getline(title, 19);
            b1.searchBook(title);
            break;

        case 4:
            cout << "\nEnter book title "
                 << "for delete record : ";
            cin.ignore();
            cin.getline(title, 19);
            b1.deleteBook(title);
            break;

        case 5:
            cout << "\nEnter book title "
                 << "to update record : ";
            cin.ignore();
            cin.getline(title, 19);
            b1.updateBook(title);
            break;

        case 6:
            cout << "\n Thanks for using";
            cout << "\n Press any key to exit";
            getch();
            exit(0);

        default:
            cout << "Invalid input";
        }
        getch();
    }
}

Output:

• Output for inserting book record using choice 1:

• Output after again inserting book record using choice 1:

• Output for inserting record 3, 4 and we can show record using the choice 2. View all book record. If “0” is appended as prefix of bookid then it is ignored as we can see in below image:

• Output for the searching book using its title name using choice 3:

• Output for updating the previously inserted data as shown below:

• Now finally it can be seen in below image “java” is updated as “JAVA” as well as book id as 4 and price as “350”. The previous data of java book in 3rd image can be seen. The record for C++ is deleted that is why it is not shown below: