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.