File.WriteAllText
Learn to write a text file with File.WriteAllText.
Writing with File.WriteAllText
The File.WriteAllText method writes a text to a file. If the file does not exist, it is created; if it exists, its content is fully replaced. Call: File.WriteAllText("out.txt", "Line 1");. The second parameter is the text to write.
This method overwrites an existing file; the old content is lost. To append instead, use File.AppendAllText. When writing is done, the file is closed automatically; no extra close call is needed.
Appending with AppendAllText
The File.AppendAllText method appends text to the end of a file; the existing content is preserved. If the file does not exist, it is created. File.AppendAllText("log.txt", "New entry\n"); adds a new line each time.
For a line break use \n or Environment.NewLine. Environment.NewLine is cross-platform: \r\n on Windows, \n on Linux. AppendAllText is common for log files.
Exercise Write and read back
Write to a file with File.WriteAllText("data.txt", "Hot day"). Then read it back with File.ReadAllText and print with Console.WriteLine.
Show example solution
First write with File.WriteAllText("data.txt", "Hot day");, then read with var text = File.ReadAllText("data.txt");, finally print with Console.WriteLine(text);.
Example solution:
using System;
using System.IO;
class Program
{
static void Main()
{
File.WriteAllText("data.txt", "Hot day");
var text = File.ReadAllText("data.txt");
Console.WriteLine(text);
}
}Test yourself
-
Complete the WriteAllText call
File.____("out.txt", "Hello");Show answer
File.WriteAllText("out.txt", "Hello"); -
What does WriteAllText do to an existing file?
- Appends to the content
- Throws an error
- Replaces the content completely
- Cannot create a new file
Show answer
Cannot create a new file — Correct. WriteAllText replaces the existing content; the old content is lost.
-
Match each method to its behavior
- WriteAllText
- Overwrites
- AppendAllText
- Appends
- ReadAllText
- Reads all
- Exists
- Checks existence