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.

Example

 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
 */

Compiling the Code

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.

Robust Programming

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.

See Also

Concepts

C# Programming Guide

Other Resources

File System and the Registry (C# Programming Guide)