C++ File Handling

File Handling

In C++, file handling is a mechanism to store the output of a program in a file and to perform various operations on it such as reading, writing, appending, etc.
Definition: File handling is the process of creating, reading, updating, and deleting files using C++ functions and classes.
File handling helps in storing data permanently and efficiently.

File Handling Operations

1. Creating and Opening Files

Using ofstream or fstream class, you can create and open a file for writing.
Example: ofstream file("example.txt");

2. Reading from Files

Using ifstream or fstream class, you can open a file for reading.
Example: ifstream file("example.txt");

3. Writing to Files

Using ofstream or fstream class, you can write data to a file.
Example: file << "Hello, World!";

4. Closing Files

After performing operations, it is important to close the file using close() function.
Example: file.close();

5. Appending to Files

To append data to a file, open it in ios::app mode using fstream class.
Example: fstream file("example.txt", ios::app);

File Handling Components

To write programs for file handling in C++ effectively, you should understand the following components:

1. Include Header Files

To perform file operations, you need to include the fstream library which contains ifstream, ofstream, and fstream classes.

Example:

  
#include <fstream>

2. Creating and Opening Files

Create and open files using ofstream (for writing), ifstream (for reading), or fstream (for both reading and writing).

Example:

  
ofstream myfile("example.txt"); // Create and open a text file

3. Writing to Files

Write data to files using the ofstream or fstream object.

Example:

  
myfile << "Hello, World!"; // Write to the file

4. Reading from Files

Read data from files using the ifstream or fstream object.

Example:

  
ifstream myfile("example.txt"); // Open a file for reading
string line;
while (getline(myfile, line)) {
    cout << line << endl; // Output the text from the file
}

5. Closing Files

Always close the file after performing operations using the close() method.

Example:

  
myfile.close(); // Close the file

6. File Modes

File modes define how a file should be opened (e.g., ios::in for reading, ios::out for writing, ios::app for appending).

Example:

  
fstream myfile;
myfile.open("example.txt", ios::out | ios::app); // Open file for writing and appending

7. Checking File Status

Before performing operations, check if a file is open and in a good state using the is_open() and good() methods.

Example:

  
if (myfile.is_open() && myfile.good()) {
    // Perform file operations
}

8. Error Handling

Handle file errors using the fail(), bad(), and eof() methods to check for specific issues.

Example:

  
if (myfile.fail()) {
    cerr << "Error opening file" << endl;
}

File Handling in C++

File Handling Example: Writing and Reading a File

  
#include <iostream>
#include <fstream>
using namespace std;

void writeToFile();  // Function prototype for writing to a file
void readFromFile(); // Function prototype for reading from a file

int main() {
    writeToFile();   // Function call to write to a file
    readFromFile();  // Function call to read from a file
    return 0;
}

// Function to write data to a file
void writeToFile() {
    ofstream outFile("example.txt"); // Create and open a text file for writing
    if (outFile.is_open()) {
        outFile << "Hello, World!\n"; // Write to the file
        outFile << "Welcome to file handling in C++.\n";
        outFile.close();              // Close the file
    } else {
        cout << "Unable to open file for writing." << endl;
    }
}

// Function to read data from a file
void readFromFile() {
    ifstream inFile("example.txt");   // Open a text file for reading
    string line;
    if (inFile.is_open()) {
        while (getline(inFile, line)) { // Read the file line by line
            cout << line << endl;      // Output the text from the file
        }
        inFile.close();                // Close the file
    } else {
        cout << "Unable to open file for reading." << endl;
    }
}

output

  
Hello, World!
Welcome to file handling in C++.

In the above program, writeToFile() is called from main() to write data to a file named example.txt.
The writeToFile() function creates and opens the file, writes two lines of text, and then closes the file.
After that, readFromFile() is called from main() to read the contents of the file.
The readFromFile() function opens the file, reads its contents line by line, and prints each line to the console, then closes the file.

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