C# File Operations, C# Input Output (C# I/O)

A file is a named collection of data stored on a storage device (like a hard disk, SSD, or USB drive). It allows data to persist even after a program stops running. Examples:

• document.txt → text data
• image.jpg → image data
• data.json → structured data

Inside a file, data is stored as:

• Text (human-readable) → .txt, .csv, .json
• Binary (machine-readable) → .exe, .jpg, .pdf

What is File I/O?

File I/O (Input/Output) means:

• Input → reading data from a file into a program
• Output → writing data from a program into a file

So File I/O is simply how a program communicates with files on disk.

Example:

• Read user data from users.txt
• Save results into output.txt

What are the file operations in C#?

In C#, file operations are actions you perform on files using the System.IO namespace.

Common file operations:

a) Create a file

File.Create("test.txt");

b) Write to a file

File.WriteAllText("test.txt", "Hello World");

c) Read from a file

string content = File.ReadAllText("test.txt");
Console.WriteLine(content);

d) Append to a file

File.AppendAllText("test.txt", "More text");

e) Delete a file

File.Delete("test.txt");

f) Work with streams (advanced)

using (StreamReader sr = new StreamReader("test.txt"))
{
string line = sr.ReadLine();
}

Required Namespaces to Enable c# File Operations

using System;
using System.IO;

How to Write File in C#?

C# Write File with TextWriter

TextWriter tw = new StreamWriter("date.txt");
tw.WriteLine(DateTime.Now);
tw.Close();

Writing to File with StreamWriter in C#

StreamWriter writer = new StreamWriter("c:\\test.txt");
writer.WriteLine("File created using StreamWriter class.");
writer.Close();

C# Flush String to File

File.WriteAllText("C:\\test.txt", "How C#");

Write String Array to File in C#

string[] howcsharp = new string[]
{
    "c#",
    "technology",
    "comparison",
    "algorithm",
    "discussion",
    "tutorial",
    "faq"
};

File.WriteAllLines("file.txt", howcsharp);

C# File operations with FileStream

FileStream F = new FileStream("test.dat", FileMode.OpenOrCreate,
                                          FileAccess.ReadWrite);
for (int i = 1; i <= 20; i++)
{
    F.WriteByte((byte)i);
}

F.Position = 0;

for (int i = 0; i <= 20; i++)
{
    Console.Write(F.ReadByte() + " ");
}

F.Close();

Using BinaryWriter to write Binary File in C#

int[] integerList = new int[] { 1, 4, 6, 7, 11, 55, 777, 23, 266, 44, 82, 93 };

using (BinaryWriter b = new BinaryWriter(File.Open("file.bin",
                                         FileMode.Create)))
{
    foreach (int i in integerList)
    {
        b.Write(i);
    }
}

How to Read From File in C#

C# Read From File with TextWriter

Textreader tr = new StreamReader("date.txt");
Console.WriteLine(tr.ReadLine());
tr.Close();

Reading From File with StreamReader in C#

using (StreamReader sr = File.OpenText("path"))
{
    string s = "";
    while ((s = sr.ReadLine()) != null)
    {
        Console.WriteLine(s);
    }
}

Read Everything From File with ReadAllText Function in C#

string file = File.ReadAllText("C:\\file.txt");
Console.WriteLine(file);

And here is the code to return file content to a list in C#:

List<string> fileLines = File.ReadAllLines("file.txt").ToList();

Counting number of lines of a file in C#:

int lineCount = File.ReadAllLines("file.txt").Length;

Example LINQ Queries with File Operations:

bool exists = (from line in File.ReadAllLines("file.txt") where
line == "Some line match" select line).Count() > 0;

Reading File Content to A String Array in C#

string[] lines = File.ReadAllLines("file.txt");
foreach (string line in lines)
{
    if (line.Length > 80)
    {
        Console.WriteLine(line);
    }
}

Getting/Printing List of Directories in C#

string[] dirs = Directory.GetDirectories("c:\\folder\");
foreach (string dir in dirs)
{
Console.WriteLine(dir);
}

Getting/Printing List of Files in a Folder in C#

string[] files = Directory.GetFiles("c:\\folder\");
foreach (string file in files)
{
Console.WriteLine(file);
}

Binary File Operations, Using BinaryReader in C# to Read Binary Files

using (BinaryReader b = new BinaryReader(File.Open("file.bin",
                                         FileMode.Open)))
{
    int pos = 0;
    int length = (int) b.BaseStream.Length;

    while (pos < length)
    {
        int v = b.ReadInt32();
        Console.WriteLine(v);

        pos += sizeof(int);
    }
}

File I/O in C# vs Other Languages

C#

• Uses System.IO library
• High-level helper methods (File.ReadAllText, File.WriteAllText)
• Also supports low-level streams (FileStream, StreamReader)
• Very structured and object-oriented

Python

with open("test.txt", "r") as f:
content = f.read()

• Very simple syntax
• Uses open() function
• File handling is very concise

Comparison: Python is easier for beginners, fewer lines of code

Java

BufferedReader br = new BufferedReader(new FileReader("test.txt"));
String line = br.readLine();

• More verbose than C#
• Uses classes like FileReader, BufferedReader
• Requires explicit exception handling

Comparison: Similar to C#, but usually more boilerplate

C / C++

FILE *fp = fopen("test.txt", "r");
fgets(buffer, 100, fp);
fclose(fp);

• Very low-level file handling
• Manual memory and pointer management
• More error-prone but very fast

Comparison: C# is safer and higher-level than C/C++