C# Read and Write Text Files

C# contains easy to use functions to read/write a text file.
Basically you can read a text file with a single line of code (if you want).

The functions are included in System.Io, so you need to add "using System.Io;" to the code.
We also need System.Text for the encodings ("using System.Text;").

The encoding of the text file is important. Common encodings are:

• Encoding.Default: Operation system current ANSI codepage
• Encoding.UTF8: utf-8 format (e.g. used for html pages)
• Encoding.Unicode: Unicode format (utf-16 little endian encoding, a.k.a. UCS-2 LE)

Encoding.UTF8 and Encoding.Unicode adds a BOM (Byte Order Mark) to the file.
The byte order mark (BOM) is a unicode character (at start), which signals the encoding of the text stream (file).

Write a String to a Text File (Unicode Encoding)

Write a string to a unicode text file using System.Io.File.WriteAllText:

using System;
using System.IO;
using System.Text;

namespace TextFileDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            string filepath = @"c:\temp\testfile.txt";
            // equals string filepath = "c:\\temp\\testfile.txt";

            string filetext = "Hello World" + Environment.NewLine + "line2" + Environment.NewLine + "line3";
            //equals string filetext = "Hello World\r\nline2\r\nline3";

            File.WriteAllText(filepath, filetext, Encoding.Unicode);
        }
    }
}

The code can be shortened to:

using System;
using System.IO;
using System.Text;

namespace TextFileDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            File.WriteAllText(@"c:\temp\testfile.txt", "Hello World\r\nline2\r\nline3", Encoding.Unicode);
        }
    }
}

The function adds a BOM (Byte Order Mark) to the file.

Write a String to a Text File (utf-8 Encoding)

Write a string to a utf-8 text file using System.Io.File.WriteAllText:

using System;
using System.IO;
using System.Text;

namespace TextFileDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            File.WriteAllText(@"c:\temp\testfile.txt", "Hello World\r\nline2\r\nline3", Encoding.UTF8);
        }
    }
}

The function adds a BOM (Byte Order Mark) to the file.

Write a String to a Text File (ANSI Encoding)

Write a string to a ANSI (current codepage) text file using System.Io.WriteAllText:

using System;
using System.IO;
using System.Text;

namespace TextFileDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            File.WriteAllText(@"c:\temp\testfile.txt", "Hello World\r\nline2\r\nline3", Encoding.Default);
            // equals File.WriteAllText(@"c:\temp\testfile.txt", "Hello World\r\nline2\r\nline3");
        }
    }
}

Read String from a Text File (Unicode, utf-8 and ANSI Encoding)

Read a string from a text file using System.Io.File.ReadAllText:

We don't need to care about the encoding, because the function detects the encoding by reading the BOM (Byte Order Mark).

using System;
using System.IO;
using System.Text;

namespace TextFileDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            string filepath = @"c:\temp\testfile.txt";
            // equals string filepath = "c:\\temp\\testfile.txt";

            // read text file
            string filetext = File.ReadAllText(filepath);

            // output text to console
            Console.WriteLine(filetext);
        }
    }
}

The code can be shortened to:

using System;
using System.IO;
using System.Text;

namespace TextFileDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            // read text file and output text to console
            Console.WriteLine(File.ReadAllText(@"c:\temp\testfile.txt"));
        }
    }
}

Read/Write Text File from/to a string array

Using a string array works basically the same way, you just need to use System.Io.File.WriteAllLines and System.Io.File.ReadAllLines.

Sample:

using System;
using System.IO;
using System.Text;

namespace TextFile
{
    class Program
    {
        static void Main(string[] args)
        {
            string filepath = @"c:\temp\testfile.txt";

            // write all text line text file to string array
            string[] textlines = { "line1", "line2", "line3" };
            File.WriteAllLines(filepath, textlines, Encoding.Unicode);

            // read all text lines to string array
            string[] readarray = File.ReadAllLines(filepath);

            // output to console (iterate string array)
            foreach (string textline in readarray)
            {
                Console.WriteLine(textline);
            }
        }
    }
}