How to: Write text to a file
This article shows different ways to write text to a file for a .NET app.
The following classes and methods are typically used to write text to a file:
StreamWriter contains methods to write to a file synchronously (Write and WriteLine) or asynchronously (WriteAsync and WriteLineAsync).
File provides static methods to write text to a file such as WriteAllLines and WriteAllText, or to append text to a file such as AppendAllLines, AppendAllText, and AppendText.
Path is for strings that have file or directory path information. It contains the Combine method and in .NET Core 2.1 and later, the Join and TryJoin methods. These methods let you concatenate strings for building a file or directory path.
Note
The following examples show only the minimum amount of code needed. A real-world app usually provides more robust error checking and exception handling.
Example: Synchronously write text with StreamWriter
The following example shows how to use the StreamWriter class to synchronously write text to a new file one line at a time. Because the StreamWriter object is declared and instantiated in a using statement, the Dispose method is invoked, which automatically flushes and closes the stream.
using System;
using System.IO;
class Program
{
static void Main(string[] args)
{
// Create a string array with the lines of text
string[] lines = { "First line", "Second line", "Third line" };
// Set a variable to the Documents path.
string docPath =
Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
// Write the string array to a new file named "WriteLines.txt".
using (StreamWriter outputFile = new StreamWriter(Path.Combine(docPath, "WriteLines.txt")))
{
foreach (string line in lines)
outputFile.WriteLine(line);
}
}
}
// The example creates a file named "WriteLines.txt" with the following contents:
// First line
// Second line
// Third line
Imports System.IO
Class WriteText
Public Shared Sub Main()
' Create a string array with the lines of text
Dim lines() As String = {"First line", "Second line", "Third line"}
' Set a variable to the Documents path.
Dim docPath As String = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
' Write the string array to a new file named "WriteLines.txt".
Using outputFile As New StreamWriter(Path.Combine(docPath, Convert.ToString("WriteLines.txt")))
For Each line As String In lines
outputFile.WriteLine(line)
Next
End Using
End Sub
End Class
' The example creates a file named "WriteLines.txt" with the following contents:
' First line
' Second line
' Third line
Example: Synchronously append text with StreamWriter
The following example shows how to use the StreamWriter class to synchronously append text to the text file created in the first example:
using System;
using System.IO;
class Program
{
static void Main(string[] args)
{
// Set a variable to the Documents path.
string docPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
// Append text to an existing file named "WriteLines.txt".
using (StreamWriter outputFile = new StreamWriter(Path.Combine(docPath, "WriteLines.txt"), true))
{
outputFile.WriteLine("Fourth Line");
}
}
}
// The example adds the following line to the contents of "WriteLines.txt":
// Fourth Line
Imports System.IO
Class AppendText
Public Shared Sub Main()
' Set a variable to the Documents path.
Dim docPath As String =
Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
' Append text to an existing file named "WriteLines.txt".
Using outputFile As New StreamWriter(Path.Combine(docPath, Convert.ToString("WriteLines.txt")), True)
outputFile.WriteLine("Fourth Line")
End Using
End Sub
End Class
' The example adds the following line to the contents of "WriteLines.txt":
' Fourth Line
Example: Asynchronously write text with StreamWriter
The following example shows how to asynchronously write text to a new file using the StreamWriter class. To invoke the WriteAsync method, the method call must be within an async method.
using System;
using System.IO;
using System.Threading.Tasks;
class Program
{
static async Task Main()
{
// Set a variable to the Documents path.
string docPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
// Write the specified text asynchronously to a new file named "WriteTextAsync.txt".
using (StreamWriter outputFile = new StreamWriter(Path.Combine(docPath, "WriteTextAsync.txt")))
{
await outputFile.WriteAsync("This is a sentence.");
}
}
}
// The example creates a file named "WriteTextAsync.txt" with the following contents:
// This is a sentence.
Imports System.IO
Public Module Example
Public Sub Main()
WriteTextAsync()
End Sub
Async Sub WriteTextAsync()
' Set a variable to the Documents path.
Dim docPath As String = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
' Write the text asynchronously to a new file named "WriteTextAsync.txt".
Using outputFile As New StreamWriter(Path.Combine(docPath, Convert.ToString("WriteTextAsync.txt")))
Await outputFile.WriteAsync("This is a sentence.")
End Using
End Sub
End Module
' The example creates a file named "WriteTextAsync.txt" with the following contents:
' This is a sentence.
Example: Write and append text with the File class
The following example shows how to write text to a new file and append new lines of text to the same file using the File class. The WriteAllText and AppendAllLines methods open and close the file automatically. If the path you provide to the WriteAllText method already exists, the file is overwritten.
using System;
using System.IO;
class Program
{
static void Main(string[] args)
{
// Create a string with a line of text.
string text = "First line" + Environment.NewLine;
// Set a variable to the Documents path.
string docPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
// Write the text to a new file named "WriteFile.txt".
File.WriteAllText(Path.Combine(docPath, "WriteFile.txt"), text);
// Create a string array with the additional lines of text
string[] lines = { "New line 1", "New line 2" };
// Append new lines of text to the file
File.AppendAllLines(Path.Combine(docPath, "WriteFile.txt"), lines);
}
}
// The example creates a file named "WriteFile.txt" with the contents:
// First line
// And then appends the following contents:
// New line 1
// New line 2
Imports System.IO
Class WriteFile
Public Shared Sub Main()
' Create a string array with the lines of text
Dim text As String = "First line" & Environment.NewLine
' Set a variable to the Documents path.
Dim docPath As String = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)
' Write the text to a new file named "WriteFile.txt".
File.WriteAllText(Path.Combine(docPath, Convert.ToString("WriteFile.txt")), text)
' Create a string array with the additional lines of text
Dim lines() As String = {"New line 1", "New line 2"}
' Append new lines of text to the file
File.AppendAllLines(Path.Combine(docPath, Convert.ToString("WriteFile.txt")), lines)
End Sub
End Class
' The example creates a file named "WriteFile.txt" with the following contents:
' First line
' And then appends the following contents:
' New line 1
' New line 2
