Use Visual C# to read from and write to a text file

This article helps you read from and write to a text file by using Visual C#.

Original product version:   Visual Studio
Original KB number:   816149

Summary

The Read a text file section of this article describes how to use the StreamReader class to read a text file. The Write a text file (example 1) and the Write a text file (example 2) sections describe how to use the StreamWriter class to write text to a file.

Read a text file

The following code uses the StreamReader class to open, to read, and to close the text file. You can pass the path of a text file to the StreamReader constructor to open the file automatically. The ReadLine method reads each line of text, and increments the file pointer to the next line as it reads. When the ReadLine method reaches the end of the file, it returns a null reference. For more information, see StreamReader Class.

  1. Create a sample text file in Notepad. Follow these steps:

    1. Paste the hello world text in Notepad.
    2. Save the file as Sample.txt.
  2. Start Microsoft Visual Studio.

  3. On the File menu, point to New, and then select Project.

  4. Select Visual C# Projects under Project Types, and then select Console Application under Templates.

  5. Add the following code at the beginning of the Class1.cs file:

    using System.IO;
    
  6. Add the following code to the Main method:

    String line;
    try
    {
        //Pass the file path and file name to the StreamReader constructor
        StreamReader sr = new StreamReader("C:\\Sample.txt");
        //Read the first line of text
        line = sr.ReadLine();
        //Continue to read until you reach end of file
        while (line != null)
        {
            //write the lie to console window
            Console.WriteLine(line);
            //Read the next line
            line = sr.ReadLine();
        }
        //close the file
        sr.Close();
        Console.ReadLine();
    }
    catch(Exception e)
    {
        Console.WriteLine("Exception: " + e.Message);
    }
    finally
    {
        Console.WriteLine("Executing finally block.");
    }
    
  7. On the Debug menu, select Start to compile and to run the application. Press ENTER to close the Console window. The Console window displays the contents of the Sample.txt file:

    Hello world
    

Write a text file (example 1)

The following code uses the StreamWriter class to open, to write, and to close the text file. In a similar way to the StreamReader class, you can pass the path of a text file to the StreamWriter constructor to open the file automatically. The WriteLine method writes a complete line of text to the text file.

  1. Start Visual Studio.

  2. On the File menu, point to New, and then select Project.

  3. Select Visual C# Projects under Project Types, and then select Console Application under Templates.

  4. Add the following code at the beginning of the Class1.cs file:

    using System.IO;
    
  5. Add the following code to the Main method:

    try
    {
        //Pass the filepath and filename to the StreamWriter Constructor
        StreamWriter sw = new StreamWriter("C:\\Test.txt");
        //Write a line of text
        sw.WriteLine("Hello World!!");
        //Write a second line of text
        sw.WriteLine("From the StreamWriter class");
        //Close the file
        sw.Close();
    }
    catch(Exception e)
    {
        Console.WriteLine("Exception: " + e.Message);
    }
    finally
    {
        Console.WriteLine("Executing finally block.");
    }
    
  6. On the Debug menu, select Start to compile and to run the application. This code creates a file that is named Test.txt on drive C. Open Test.txt in a text editor such as Notepad. Test.txt contains two lines of text:

    Hello World!!
    From the StreamWriter class
    

Write a text file (example 2)

The following code uses the StreamWriter class to open, to write, and to close the text file. Unlike the previous example, this code passes two additional parameters to the constructor. The first parameter is the file path and the file name of the file. The second parameter, true, specifies that the file is opened in append mode. If you specify false for the second parameter, the contents of the file are overwritten each time you run the code. The third parameter specifies Unicode, so that StreamWriter encodes the file in Unicode format. You can also specify the following encoding methods for the third parameter:

  • ASC11
  • Unicode
  • UTF7
  • UTF8

The Write method is similar to the WriteLine method, except that the Write method doesn't automatically embed a carriage return or line feed (CR/LF) character combination. It's useful when you want to write one character at a time.

  1. Start Visual Studio.

  2. On the File menu, point to New, and then click Project.

  3. Click Visual C# Projects under Project Types, and then click Console Application under Templates.

  4. Add the following code at the beginning of the Class1.cs file:

    using System.IO;
    using System.Text;
    
  5. Add the following code to the Main method:

    Int64 x;
    try
    {
        //Open the File
        StreamWriter sw = new StreamWriter("C:\\Test1.txt", true, Encoding.ASCII);
    
        //Write out the numbers 1 to 10 on the same line.
        for(x=0; x < 10; x++)
        {
        sw.Write(x);
        }
    
        //close the file
        sw.Close();
    }
    catch(Exception e)
    {
        Console.WriteLine("Exception: " + e.Message);
    }
    finally
    {
        Console.WriteLine("Executing finally block.");
    }
    
  6. On the Debug menu, select Start to compile and to run the application. This code creates a file that is named Test1.txt on drive C. Open Test1.txt in a text editor such as Notepad. Test1.txt contains a single line of text: 0123456789.

Complete code listing for how to read a text file

//Read a Text File
using System;
using System.IO;
namespace readwriteapp
{
    class Class1
    {
        [STAThread]
        static void Main(string[] args)
        {
            String line;
            try
            {
                //Pass the file path and file name to the StreamReader constructor
                StreamReader sr = new StreamReader("C:\\Sample.txt");
                //Read the first line of text
                line = sr.ReadLine();
                //Continue to read until you reach end of file
                while (line != null)
                {
                    //write the lie to console window
                    Console.WriteLine(line);
                    //Read the next line
                    line = sr.ReadLine();
                }
                //close the file
                sr.Close();
                Console.ReadLine();
            }
            catch(Exception e)
            {
                Console.WriteLine("Exception: " + e.Message);
            }
            finally
            {
                Console.WriteLine("Executing finally block.");
            }
        }
    }
}

Complete code listing for how to write a text file (version 1)

//Write a text file - Version-1
using System;
using System.IO;
namespace readwriteapp
{
    class Class1
    {
        [STAThread]
        static void Main(string[] args)
        {
            try
            {
                //Pass the filepath and filename to the StreamWriter Constructor
                StreamWriter sw = new StreamWriter("C:\\Test.txt");
                //Write a line of text
                sw.WriteLine("Hello World!!");
                //Write a second line of text
                sw.WriteLine("From the StreamWriter class");
                //Close the file
                sw.Close();
            }
            catch(Exception e)
            {
                Console.WriteLine("Exception: " + e.Message);
            }
            finally
            {
                Console.WriteLine("Executing finally block.");
            }
        }
    }
}

Complete code listing for how to write a text file (version 2)

//Write a text file - Version 2
using System;
using System.IO;
using System.Text;
namespace readwriteapp
{
    class Class1
    {
        [STAThread]
        static void Main(string[] args)
        {
            Int64 x;
            try
            {
                //Open the File
                StreamWriter sw = new StreamWriter("C:\\Test1.txt", true, Encoding.ASCII);
                //Writeout the numbers 1 to 10 on the same line.
                for(x=0; x < 10; x++)
                {
                    sw.Write(x);
                }
                //close the file
                sw.Close();
            }
            catch(Exception e)
            {
                Console.WriteLine("Exception: " + e.Message);
            }
            finally
            {
                Console.WriteLine("Executing finally block.");
            }
        }
    }
}

Troubleshoot

For all file manipulations, it's good programming practice to wrap the code inside a try-catch-finally block to handle errors and exceptions. Specifically, you may want to release handles to the file in the final block so that the file isn't locked indefinitely. Some possible errors include a file that doesn't exist, or a file that is already in use.