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How to: Write to a Text File (C# Programming Guide)

These examples show various ways to write text to a file. The first two examples use static methods on the System.IO.File class to write either a complete array of strings or a complete string to a text file. Example #3 shows how to add text to a file when you have to process each line individually before writing to the file. Examples 1-3 all overwrite all existing content in the file. Example #4 shows how to append text to an existing file.


    class WriteTextFile
    {
        static void Main()
        {

            // These examples assume a "C:\Users\Public\TestFolder" folder on your machine.
            // You can modify the path if necessary.

            // Example #1: Write an array of strings to a file.
            // Create a string array that consists of three lines.
            string[] lines = {"First line", "Second line", "Third line"};
            System.IO.File.WriteAllLines(@"C:\Users\Public\TestFolder\WriteLines.txt", lines);


            // Example #2: Write one string to a text file.
            string text = "A class is the most powerful data type in C#. Like structures, " +
                           "a class defines the data and behavior of the data type. ";
            System.IO.File.WriteAllText(@"C:\Users\Public\TestFolder\WriteText.txt", text);

            // Example #3: Write only some strings in an array to a file.
            using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:\Users\Public\TestFolder\WriteLines2.txt"))
            {
                foreach (string line in lines)
                {
                    if (line.Contains("Second") == false)
                    {
                        file.WriteLine(line);
                    }
                }
            }

            // Example #4: Append new text to an existing file
            using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:\Users\Public\TestFolder\WriteLines2.txt", true))
            {
                file.WriteLine("Fourth line");
            }  
        }
    }
    /* Output (to WriteLines.txt):
        First line
        Second line
        Third line

     Output (to WriteText.txt):
        A class is the most powerful data type in C#. Like structures, a class defines the data and behavior of the data type.

     Output to WriteLines2.txt after Example #3:
        First line
        Third line

     Output to WriteLines2.txt after Example #4:
        First line
        Third line
        Fourth line
     */



Copy the code into a console application.

Replace "c:\testdir" with an actual folder name on your computer, or create a folder by that name.

The following conditions may cause an exception:

  • The file exists and is read-only.

  • The path name may be too long.

  • The disk may be full.

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