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Path.ChangeExtension Method

Changes the extension of a path string.

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

public static string ChangeExtension(
	string path,
	string extension
)

Parameters

path
Type: System.String

The path information to modify. The path cannot contain any of the characters defined in GetInvalidPathChars.

extension
Type: System.String

The new extension (with or without a leading period). Specify null to remove an existing extension from path.

Return Value

Type: System.String
The modified path information.
On Windows-based desktop platforms, if path is null or an empty string (""), the path information is returned unmodified. If extension is null, the returned string contains the specified path with its extension removed. If path has no extension, and extension is not null, the returned path string contains extension appended to the end of path.

ExceptionCondition
ArgumentException

path contains one or more of the invalid characters defined in GetInvalidPathChars.

If neither path nor extension contains a period (.), ChangeExtension adds the period.

The extension parameter can contain multiple periods and any valid path characters, and can be any length. If extension is null, the returned string contains the contents of path with the last period and all characters following it removed.

If extension is an empty string, the returned path string contains the contents of path with any characters following the last period removed.

If path does not have an extension and extension is not null, the returned string contains path followed by extension.

If extension is not null and does not contain a leading period, the period is added.

If path contains a multiple extension separated by multiple periods, the returned string contains the contents of path with the last period and all characters following it replaced by extension. For example, if path is "\Dir1\examples\pathtests.csx.txt" and extension is "cs", the modified path is "\Dir1\examples\pathtests.csx.cs".

It is not possible to verify that the returned results are valid in all scenarios. For example, if path is empty, extension is appended.

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

The following code example demonstrates a use of the ChangeExtension method.

using System;
using System.IO;

public class PathSnippets
{

    public void ChangeExtension()
    {
        string goodFileName = @"C:\mydir\myfile.com.extension";
        string badFileName = @"C:\mydir\";
        string result;

        result = Path.ChangeExtension(goodFileName, ".old");
        Console.WriteLine("ChangeExtension({0}, '.old') returns '{1}'",
            goodFileName, result); 

        result = Path.ChangeExtension(goodFileName, "");
        Console.WriteLine("ChangeExtension({0}, '') returns '{1}'", 
            goodFileName, result); 

        result = Path.ChangeExtension(badFileName, ".old");
        Console.WriteLine("ChangeExtension({0}, '.old') returns '{1}'", 
            badFileName, result); 

        // This code produces output similar to the following: 
        // 
        // ChangeExtension(C:\mydir\myfile.com.extension, '.old') returns 'C:\mydir\myfile.com.old' 
        // ChangeExtension(C:\mydir\myfile.com.extension, '') returns 'C:\mydir\myfile.com.' 
        // ChangeExtension(C:\mydir\, '.old') returns 'C:\mydir\.old'

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

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

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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