How to achieve the File Handling

For achieving file handling we need to follow the following steps:- STEP 1-Naming a file STEP 2-Opening a file STEP 3-Writing data into the file STEP 4-Reading data from the file STEP 5-Closing a file.
Opening and Closing a File

In order to work with files, we first need to open them. In C++, we can open a file using the ofstream and ifstream classes. For example, here's how we can open a file using ofstream: std::ofstream my_file("example.txt"); Here, my_file - the name of the object of the ofstream class. example.txt - the name and extension of the file we want to open. Note: We can also use the open() function to open a file. For example, std::ofstream my_file.open("example.txt"); Closing a File Once we're done working with a file, we need to close it using the close() function. my_file.close();
Check the File for Errors

In file handling, it's important to ensure the file was opened without any error before we can perform any further operations on it.There are three common ways to check files for errors: 1. By Checking the File Object ofstream my_file("example.txt"); // check if the file has been opened properly if (!my_file) { // print error message cout << "Error opening the file." << endl; // terminate the main() function return 1; } if (!my_file) {...} This method checks if the file is in an error state by evaluating the file object itself. If the file has been opened successfully, the condition evaluates to true. If there's an error, it evaluates to false, and you can handle the error accordingly.
Using the is_open() Function

The is_open() function returns true - if the file was opened successfully. false - if the file failed to open or if it is in a state of error. For example, ofstream my_file("example.txt"); if (!my_file.is_open()) { cout << "Error opening the file." << endl; return 1; }
Using the fail() Function

The fail() function returns true - if the file failed to open or if it is in a state of error. false - if the file was opened successfully. ofstream my_file("example.txt"); if (my_file.fail()) { cout << "Error opening the file." << endl; return 1; }
Read From a File

Reading from text files is done by opening the file using the ifstream class. For example, ifstream my_file("example.txt"); Then, we need to read the file line-by-line. To do this, we need to loop through each line of the file until all the lines are read, i.e., until we reach the end of the file. We use the eof() function for this purpose, which returns true - if the file pointer points to the end of the file false - if the file pointer doesn't point to the end of the file
Example 2: Read From a File

using namespace std; int main() { // open a text file for reading ifstream my_file("example.txt"); // check the file for errors if(!my_file) { cout << "Error: Unable to open the file." << endl; return 1; } // store the contents of the file in "line" string string line; // loop until the end of the text file while (!my_file.eof()) { // store the current line of the file // in the "line" variable getline(my_file, line); // print the line variable cout << line << endl; } // close the file my_file.close(); return 0; }
Write to a File

#include <iostream> #include <fstream> using namespace std; int main() { // open a text file for writing ofstream my_file("example.txt"); // check the file for errors if(!my_file) { cout << "Error: Unable to open the file." << endl; return 1; } // write multiple lines to the file my_file << "Line 1" << endl; my_file << "Line 2" << endl; my_file << "Line 3" << endl; // close the file my_file.close(); return 0; } cout << "Line1" << endl; In file handling, we just replace cout with the file object to write to the file instead of the console. Our particular code will write the following text to example.txt: Line1 Line2 Line3
Append to a Text File

To add/append to the existing content of a file, you need to open the file in append mode. In C++, you can achieve this by using the ios::app flag when opening the file: ofstream my_file("example.txt", ios::app); Now, let's add some more text to the existing content of example.txt: #include <iostream> #include <fstream> using namespace std; int main() { // open a text file for appending ofstream my_file("example.txt", ios::app); // if the file doesn't open successfully, print an error message if(!my_file) { cout << "Failed to open the file for appending." << endl; return 1; } // append multiple lines to the file my_file << "Line 4" << endl; my_file << "Line 5" << endl; my_file << "Line 6" << endl; // close the file my_file.close(); return 0; } This will add the following lines to example.txt: Line 4 Line 5 Line 6
File Handling With fstream

Instead of using ifstream to read from a file and ofstream to write to the file, we can simply use the fstream class for all file operations. The constructor for fstream allows you to specify the file name and the mode for file operations. Mode Description ios::in Opens the file to read (default for ifstream). ios::out Opens the file to write (default for ofstream). ios::app Opens the file and appends new content to itat the end. #include <iostream> #include <fstream> using namespace std; int main() { // 1. write to a text file fstream my_file("example.txt", ios::out); if (my_file) { my_file << "This is a test line." << endl; my_file.close(); } else { cout << "Unable to open file for writing." << endl; return 1; } // 2. read from the same file string line; my_file.open("example.txt", ios::in); if (my_file) { while (!my_file.eof()) { getline(my_file, line); cout << "Read from file: " << line << endl; } my_file.close(); } else { cout << "Unable to open file for reading." << endl; return 1; } // 3. append data to the end of the file my_file.open("example.txt", ios::app); if (my_file) { my_file << "This is another test line, appended to the file." << endl; my_file.close(); } else { cout << "Unable to open file for appending." << endl; return 1; } return 0; }

Requirement

Files are used to store data in a storage device permanently. File handling provides a mechanism to store the output of a program in a file and to perform various operations on it. A stream is an abstraction that represents a device on which operations of input and output are performed.

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Files are used to store data in a storage device permanently. File handling provides a mechanism to store the output of a program in a file and to perform various operations on it. A stream is an abstraction that represents a device on which operations of input and output are performed.

File Handling in cplusplus part-2