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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 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" };
        // WriteAllLines creates a file, writes a collection of strings to the file, 
        // and then closes the file.
        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 a structure, " +
                       "a class defines the data and behavior of the data type. ";
        // WriteAllText creates a file, writes the specified string to the file, 
        // and then closes the file.
        System.IO.File.WriteAllText(@"C:\Users\Public\TestFolder\WriteText.txt", text);

        // Example #3: Write only some strings in an array to a file. 
        // The using statement automatically closes the stream and calls  
        // IDisposable.Dispose on the stream object. 
        using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:\Users\Public\TestFolder\WriteLines2.txt"))
        {
            foreach (string line in lines)
            {
                // If the line doesn't contain the word 'Second', write the line to the file. 
                if (!line.Contains("Second"))
                {
                    file.WriteLine(line);
                }
            }
        }

        // Example #4: Append new text to an existing file. 
        // The using statement automatically closes the stream and calls  
        // IDisposable.Dispose on the stream object. 
        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 a structure, 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

These examples all write string literals to files, but more likely you will want to use the Format method, which has many controls for writing different types of values right or left justified in a field, with or without padding, and so on.

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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