Reading text files in C#

last modified April 22, 2025

This tutorial demonstrates various methods for reading text files in C#, focusing on efficient stream-based techniques.

In C#, input and output operations rely on streams. The Stream class serves as an abstract base for all streams, representing a sequence of bytes from sources like files, I/O devices, inter-process pipes, or TCP/IP sockets.

C# stream

The Stream class provides a unified interface for input and output, abstracting away operating system and device-specific details. For example, MemoryStream handles in-memory data, while FileStream manages file-based data.

The Battle of Thermopylae was fought between an alliance of Greek city-states,
led by King Leonidas of Sparta, and the Persian Empire of Xerxes I over the
course of three days, during the second Persian invasion of Greece.

The examples in this tutorial read from this sample text file.

C# read text file with File.ReadLines

The File.ReadLines method returns an IEnumerable of a file's lines, closing the file after iteration. It is memory-efficient, ideal for large files compared to methods loading entire contents at once.

using System.Text;

var path = "thermopylae.txt";

var enumLines = File.ReadLines(path, Encoding.UTF8);

foreach (var line in enumLines)
{
    Console.WriteLine(line);
}

This example iterates over the file's lines using a foreach loop, printing each line to the console efficiently.

C# read text file with File.ReadAllLines

The File.ReadAllLines method reads all lines of a text file into a string array and closes the file automatically.

using System.Text;

var path = "thermopylae.txt";

string[] lines = File.ReadAllLines(path, Encoding.UTF8);

foreach (string line in lines)
{
    Console.WriteLine(line);
}

This example reads the entire thermopylae.txt file into a string array and prints each line to the console.

foreach (string line in lines)
{
    Console.WriteLine(line);
}

The string array is iterated to display each line, processing the file's contents in memory.

C# read text file with File.ReadAllText

The File.ReadAllText method reads a text file's entire contents into a single string and closes the file.

using System.Text;

var path = "thermopylae.txt";

string content = File.ReadAllText(path, Encoding.UTF8);
Console.WriteLine(content);

This example reads the full contents of thermopylae.txt into a string and outputs it to the console.

C# reading text file with StreamReader

The StreamReader class is designed for reading character data in a specific encoding, optimized for processing text files line by line or in full.

Using StreamReader's ReadToEnd

The ReadToEnd method reads all characters from the current stream position to the end, returning the content as a string.

using System.Text;

var path = "thermopylae.txt";

using var fs = new FileStream(path, FileMode.Open, FileAccess.Read);
using var sr = new StreamReader(fs, Encoding.UTF8);

string content = sr.ReadToEnd();

Console.WriteLine(content);

This example uses StreamReader with ReadToEnd to read the entire file content via a FileStream.

using var fs = new FileStream(path, FileMode.Open, FileAccess.Read);

The FileStream class creates a stream for file operations, supporting both synchronous and asynchronous access with specified mode and permissions.

using var sr = new StreamReader(fs, Encoding.UTF8);

The FileStream is passed to StreamReader, enabling text reading with UTF-8 encoding.

string content = sr.ReadToEnd();

The ReadToEnd method retrieves all characters from the stream's current position to its end.

Using File.OpenRead

The File.OpenRead method provides a convenient way to create a FileStream for reading.

using System.Text;

var path = "thermopylae.txt";

using var fs = File.OpenRead(path);
using var sr = new StreamReader(fs, Encoding.UTF8);

string content = sr.ReadToEnd();

Console.WriteLine(content);

This example uses File.OpenRead to create a FileStream, which is read by StreamReader using ReadToEnd.

Using StreamReader's ReadLine

The ReadLine method reads a single line from the stream, returning it as a string, ideal for line-by-line processing.

using System.Text;

var path = "thermopylae.txt";

using var fs = new FileStream(path, FileMode.Open, FileAccess.Read);
using var sr = new StreamReader(fs, Encoding.UTF8);

string line = String.Empty;

while ((line = sr.ReadLine()) != null)
{
    Console.WriteLine(line);
}

This example reads thermopylae.txt line by line using StreamReader's ReadLine method.

string line = String.Empty;

while ((line = streamReader.ReadLine()) != null)
{
        Console.WriteLine(line);
}

A while loop reads each line using ReadLine, printing it until the end of the file is reached.

C# read text with File.OpenText

The File.OpenText method opens a UTF-8 encoded text file for reading, simplifying StreamReader creation.

using System.Text;

var path = "thermopylae.txt";

using StreamReader sr = File.OpenText(path);
string content = sr.ReadToEnd();

Console.WriteLine(content);

This example uses File.OpenText to open a text file and reads its contents with ReadToEnd.

C# read text file asynchronously with StreamReader's ReadToEndAsync

The ReadToEndAsync method asynchronously reads all characters from the stream's current position to its end, returning a string.

using System.Text;

var path = "thermopylae.txt";

using var fs = new FileStream(path, FileMode.Open, FileAccess.Read);
using var sr = new StreamReader(fs, Encoding.UTF8);

string content = await sr.ReadToEndAsync();
Console.WriteLine(content);

This example reads a text file asynchronously using ReadToEndAsync, improving performance for I/O-bound operations.

string content = await sr.ReadToEndAsync();

The await operator pauses execution until the asynchronous ReadToEndAsync task completes, ensuring non-blocking operation.

C# read text file with buffered StreamReader

This example demonstrates reading a large text file using a buffered StreamReader with a custom buffer size for optimized performance.

using System.Text;

var path = "thermopylae.txt";

using var fs = new FileStream(path, FileMode.Open, FileAccess.Read);
using var sr = new StreamReader(fs, Encoding.UTF8, true, 1024);

string line;
while ((line = sr.ReadLine()) != null)
{
    Console.WriteLine(line);
}

This example uses a StreamReader with a 1KB buffer to read thermopylae.txt line by line, optimizing memory usage for large files.

C# read text file with async ReadLineAsync

The ReadLineAsync method reads a line asynchronously, enhancing performance for line-by-line processing in I/O-bound applications.

using System.Text;

var path = "thermopylae.txt";

using var fs = File.OpenRead(path);
using var sr = new StreamReader(fs, Encoding.UTF8);

string line;
while ((line = await sr.ReadLineAsync()) != null)
{
    Console.WriteLine(line);
}

This example reads thermopylae.txt line by line asynchronously using ReadLineAsync, ensuring efficient non-blocking I/O.

C# read text file with TextReader

The TextReader class, base of StreamReader, provides a generic way to read text, useful for abstracting text sources.

using System.Text;

var path = "thermopylae.txt";

using TextReader reader = File.OpenText(path);
string content = reader.ReadToEnd();

Console.WriteLine(content);

This example uses TextReader via File.OpenText to read the entire thermopylae.txt file, demonstrating a flexible text reading approach.

C# read text file with error handling

This example shows how to handle file reading errors, ensuring robust file I/O operations with proper exception management.

using System.Text;

var path = "thermopylae.txt";

try
{
    using var fs = File.OpenRead(path);
    using var sr = new StreamReader(fs, Encoding.UTF8);

    string content = sr.ReadToEnd();
    Console.WriteLine(content);
}
catch (FileNotFoundException)
{
    Console.WriteLine("Error: The file was not found.");
}
catch (IOException ex)
{
    Console.WriteLine($"Error reading file: {ex.Message}");
}
catch (Exception ex)
{
    Console.WriteLine($"Unexpected error: {ex.Message}");
}

This example wraps file reading in a try-catch block, handling specific exceptions like FileNotFoundException and IOException to ensure robust error reporting.

Source

File and Stream I/O

This article explored multiple techniques for reading text files in C#, including synchronous and asynchronous methods.

Author

I am Jan Bodnar, a dedicated programmer with extensive experience in software development. Since 2007, I have authored over 1,400 programming articles and eight e-books. With more than a decade of teaching programming, I share my expertise through comprehensive tutorials.

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