File Streams in C++ (ifstream, ofstream, fstream)

In any real-world application, handling data externally—outside of memory—is crucial. Whether you’re storing logs, user input, or configuration files, File Streams in C++ allow you to seamlessly interact with files.

With the expert guidance of Kamlesh Singad at Code With Kamlesh, this blog simplifies Strings & File Handling by diving deep into file streams using ifstream, ofstream, and fstream.

What Are File Streams?

A file stream is a mechanism in C++ that connects your program with an external file. It works like a flow of data:

• Input File Stream (ifstream): Read data from files
• Output File Stream (ofstream): Write data to files
• File Stream (fstream): For both reading and writing

Also Read: Conditional Statements in C/C++: Mastering if, else if, and switch-case

Why Use File Streams in C++?

C++ file streams offer:

• Type safety and error handling
• Object-oriented approach to file I/O
• Built-in support for strings and formatted data
• Easier syntax compared to C’s FILE pointer method

Understanding the <fstream> Library

Include this in your program:

#include <fstream>

It gives access to three classes:

• ifstream
• ofstream
• fstream

All these classes inherit from istream, ostream, or both.

Opening and Closing Files

To open:

ofstream outFile("data.txt"); // Opens in write mode
ifstream inFile("data.txt");  // Opens in read mode

To close:

outFile.close();
inFile.close();

Checking File Opening Success

ifstream file("info.txt");
if (!file) {
    cerr << "Error opening file!";
}

Or using:

if (file.is_open()) {
    // proceed
}

Also Read: Operators in C/C++: Arithmetic, Logical, Relational & Bitwise

Writing to Files Using ofstream

ofstream file("output.txt");
file << "Welcome to File Streams in C++!" << endl;
file.close();

Reading from Files Using ifstream

ifstream file("output.txt");
string line;
while (getline(file, line)) {
    cout << line << endl;
}
file.close();

Using fstream for Both Reading and Writing

fstream file("data.txt", ios::in | ios::out);
file << "Hello, Kamlesh!" << endl;
file.seekg(0);
string line;
getline(file, line);
cout << "Read: " << line << endl;
file.close();

File Opening Modes

Mode	Description
ios::in	Read
ios::out	Write
ios::app	Append
ios::trunc	Truncate existing
ios::binary	Binary file

Reading Word by Word / Character by Character

string word;
while (file >> word) {
    cout << word << endl;
}

Or:

char ch;
while (file.get(ch)) {
    cout << ch;
}

Formatted Output with ofstream

#include <iomanip>
file << setw(10) << left << "Name" << setw(5) << "Age";

File Positioning with seekg and seekp

file.seekg(0);         // Move to beginning
file.seekp(ios::end);  // Move to end for writing

Also Read: Understanding Data Types and Variables in C/C++

Error Handling with File Streams

if (file.fail()) {
    cerr << "File operation failed.";
}

For exception-based:

file.exceptions(ifstream::failbit | ifstream::badbit);
try {
    file.open("data.txt");
} catch (ifstream::failure& e) {
    cerr << "Exception opening file: " << e.what();
}

Practical Example: Student Record System

struct Student {
    int roll;
    string name;
};

void writeStudent(Student s) {
    ofstream file("students.txt", ios::app);
    file << s.roll << " " << s.name << endl;
    file.close();
}

void readStudents() {
    ifstream file("students.txt");
    Student s;
    while (file >> s.roll >> s.name) {
        cout << s.roll << " - " << s.name << endl;
    }
    file.close();
}

FAQs

What’s the difference between ifstream and fstream?
ifstream is for reading only, while fstream supports both reading and writing.

How do you open a file for appending?
Use ofstream file("log.txt", ios::app);

What happens if you don’t close a file?
It may lead to memory leaks or data not being written properly.

Can I use strings with file streams?
Yes, you can easily read and write std::string with streams.

How do I check if a file exists in C++?
Attempt to open it with ifstream. If file.fail() is true, it doesn’t exist.

Is it better to use fstream over C’s FILE?*
Yes, fstream is safer, more flexible, and C++-oriented.

Conclusion

With ifstream, ofstream, and fstream, C++ offers an intuitive and powerful system for handling files. By learning through examples provided by Kamlesh Singad at Code With Kamlesh, you’re now capable of integrating Strings & File Handling with modern C++ practices.

Keep experimenting and build real-world applications like loggers, file readers, and database systems using file streams!