Append to File

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

int main() {
    // Open file in append mode
    ofstream outFile("data.txt", ios::app);
    
    if (outFile.is_open()) {
        // Append data to existing file
        outFile << "\nAppended line 1" << endl;
        outFile << "Appended line 2" << endl;
        outFile << "Appended line 3" << endl;
        
        outFile.close();
        cout << "Data appended to file successfully!" << endl;
    } else {
        cout << "Error: Unable to open file for appending." << endl;
    }
    
    // Read and display updated file
    ifstream inFile("data.txt");
    if (inFile.is_open()) {
        string line;
        cout << "\nUpdated file contents:" << endl;
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close();
    }
    
    return 0;
}

Data appended to file successfully!

Updated file contents:
Hello, World!
This is a C++ file handling program.
Line 3: Learning file operations.
100 200 300
Appended line 1
Appended line 2
Appended line 3

This program teaches you how to Append to a File in C++. Appending adds data to the end of an existing file without overwriting the original content. This is essential for logging, adding records, and preserving existing data.

---

1. What This Program Does

The program demonstrates file appending operations:

• Opening file in append mode using ios::app
• Adding data to end of existing file
• Preserving original file content
• Verifying appended content

File appending enables adding data without losing existing content.

---

2. Header Files Used

1. #include <iostream>

   • Provides cout and cin for input/output operations.

2. #include <fstream>

   • Provides file stream classes (ofstream, ifstream).

---

3. Understanding File Appending

Append Mode Concept:

• Adds data to end of file
• Preserves existing content
• File pointer starts at end
• Creates file if doesn't exist

File Modes:

• ios::app: append mode (adds to end)
• ios::out: write mode (overwrites, default)
• ios::in: read mode
• Can combine: ios::app | ios::out

---

4. Opening File in Append Mode

Using ios::app:

ofstream outFile("data.txt", ios::app);

How it works:

• Opens file in append mode
• File pointer at end of file
• New data added after existing
• Creates file if doesn't exist

Checking Success:

if (outFile.is_open()) { // File opened successfully }

---

5. Appending Data

Writing in Append Mode:

outFile << "\nAppended line 1" << endl; outFile << "Appended line 2" << endl;

How it works:

• Data written at end of file
• Existing content preserved
• Newlines separate additions
• Sequential appending

---

6. Verifying Appended Content

Reading File:

ifstream inFile("data.txt"); string line; while (getline(inFile, line)) { cout << line << endl; }

How it works:

• Read entire file
• Shows original + appended content
• Verifies append operation
• Confirms data preservation

---

7. When to Use Append Mode

Best For:

• Logging events
• Adding records
• Preserving existing data
• Building files incrementally
• Appending to logs

Example Scenarios:

• Event logging
• Adding user data
• Building reports
• Appending to logs
• Incremental data collection

---

8. Important Considerations

Append vs Write:

• Append: adds to end (preserves data)
• Write: overwrites (loses data)
• Choose based on requirement
• Be careful with mode selection

File Position:

• Append mode: pointer at end
• Write mode: pointer at beginning
• New data always added at end in append
• Cannot insert in middle

Newlines:

• Add newlines between appends
• Use endl or "\n"
• Maintains file formatting
• Prevents data concatenation

---

9. return 0;

This ends the program successfully.

---

Summary

• File appending: uses ios::app mode flag with ofstream to add data to end of file.
• Preserves existing content, adds new data after original content.
• File pointer starts at end, new data appended sequentially.
• Creates file if doesn't exist, preserves content if exists.
• Understanding file appending enables incremental data addition.
• Essential for logging, adding records, and preserving existing files.

This program is fundamental for learning file modes, understanding data preservation, and preparing for logging and incremental file operations in C++ programs.