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AppendText Method

File.AppendText Method

Creates a StreamWriter that appends UTF-8 encoded text to an existing file, or to a new file if the specified file does not exist.

Namespace:  System.IO
Assembly:  mscorlib (in mscorlib.dll)

public static StreamWriter AppendText(
	string path
)

Parameters

path
Type: System.String

The path to the file to append to.

Return Value

Type: System.IO.StreamWriter
A stream writer that appends UTF-8 encoded text to the specified file or to a new file.

ExceptionCondition
UnauthorizedAccessException

The caller does not have the required permission.

ArgumentException

path is a zero-length string, contains only white space, or contains one or more invalid characters as defined by InvalidPathChars.

ArgumentNullException

path is null.

PathTooLongException

The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.

DirectoryNotFoundException

The specified path is invalid (for example, the directory doesn’t exist or it is on an unmapped drive).

NotSupportedException

path is in an invalid format.

This method is equivalent to the StreamWriter(String, Boolean) constructor overload. If the file specified by path does not exist, it is created. If the file does exist, write operations to the StreamWriter append text to the file. Additional threads are permitted to read the file while it is open.

The path parameter is permitted to specify relative or absolute path information. Relative path information is interpreted as relative to the current working directory. To obtain the current working directory, see GetCurrentDirectory.

The path parameter is not case-sensitive.

For a list of common I/O tasks, see Common I/O Tasks.

The following example appends text to a file. The method creates a new file if the file doesn’t exist. However, the directory named temp on drive C must exist for the example to complete successfully.

using System;
using System.IO;

class Test 
{
    public static void Main() 
    {
        string path = @"c:\temp\MyTest.txt";
        // This text is added only once to the file. 
        if (!File.Exists(path)) 
        {
            // Create a file to write to. 
            using (StreamWriter sw = File.CreateText(path)) 
            {
                sw.WriteLine("Hello");
                sw.WriteLine("And");
                sw.WriteLine("Welcome");
            }	
        }

        // This text is always added, making the file longer over time 
        // if it is not deleted. 
        using (StreamWriter sw = File.AppendText(path)) 
        {
            sw.WriteLine("This");
            sw.WriteLine("is Extra");
            sw.WriteLine("Text");
        }	

        // Open the file to read from. 
        using (StreamReader sr = File.OpenText(path)) 
        {
            string s = "";
            while ((s = sr.ReadLine()) != null) 
            {
                Console.WriteLine(s);
            }
        }
    }
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

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