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AppendAllText Method (String, String)
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File.AppendAllText Method (String, String)

Opens a file, appends the specified string to the file, and then closes the file. If the file does not exist, this method creates a file, writes the specified string to the file, then closes the file.

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

public static void AppendAllText(
	string path,
	string contents
)

Parameters

path
Type: System.String

The file to append the specified string to.

contents
Type: System.String

The string to append to the file.

ExceptionCondition
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).

IOException

An I/O error occurred while opening the file.

UnauthorizedAccessException

path specified a file that is read-only.

-or-

This operation is not supported on the current platform.

-or-

path specified a directory.

-or-

The caller does not have the required permission.

NotSupportedException

path is in an invalid format.

SecurityException

The caller does not have the required permission.

Given a string and a file path, this method opens the specified file, appends the string to the end of the file, and then closes the file. The file handle is guaranteed to be closed by this method, even if exceptions are raised.

The method creates the file if it doesn’t exist, but it doesn't create new directories. Therefore, the value of the path parameter must contain existing directories.

The following code example demonstrates the use of the AppendAllText method to add extra text to the end of a file. In this example, a file is created if it doesn't already exist, and text is added to it. However, the directory named temp on drive C must exist for the example to complete successfully.

using System;
using System.IO;
using System.Text;

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. 
            string createText = "Hello and Welcome" + Environment.NewLine;
            File.WriteAllText(path, createText);
        }

        // This text is always added, making the file longer over time 
        // if it is not deleted. 
        string appendText = "This is extra text" + Environment.NewLine;
        File.AppendAllText(path, appendText);

        // Open the file to read from. 
        string readText = File.ReadAllText(path);
        Console.WriteLine(readText);
    }
}

.NET Framework

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

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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