How to Find the Extension of a File in C#

How to find the extension of a file in C#?

Path.GetExtension

string myFilePath = @"C:\MyFile.txt";
string ext = Path.GetExtension(myFilePath);
// ext would be ".txt"

Get File Extension C#

You can use Directory.EnumerateFiles() like this:

string path = "F:\\WorkingCopy\\files\\";
string filename = ddl.SelectedItem.Text;

string existingFile = Directory.EnumerateFiles(path, filename + ".*").FirstOrDefault();

if (!string.IsNullOrEmpty(existingFile))
    Console.WriteLine("Extension is: " + Path.GetExtension(existingFile));

Directory.EnumerateFiles searches the path for files like filename.*. Path.GetExtension() returns the extension of the found file.

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In general, I prefer to use EnumerateFiles() instead of GetFiles because it returns an IEnumerable<string> instead string[]. This suggests that it only returns the matching files as needed instead searching all matching files at once. (This doesn't really matter in your case, just a general note).

How to know the extension of documents/files?

You may use the MimeMapping.GetMimeMapping method the mime type of the document. With that,you do not really need to get the file extension and write those if condition for all the different types.

var fileName = Path.GetFileName("SomeFileNameWithLongPath.pdf");
string mimeType= MimeMapping.GetMimeMapping(fileName );

If you really want the extension, you can use the Path.GetExtension method

var extension = Path.GetExtension("SomeFileNameWithLongPath.pdf");

Find a file with a certain extension in folder

Look at the System.IO.Directory class and the static method GetFiles. It has an overload that accepts a path and a search pattern. Example:

 string[] files = System.IO.Directory.GetFiles(path, "*.txt");

A quick way to search for file extensions in C#

Fastest would be:

Process p = new Process();
p.StartInfo.UseShellExecute = false;
p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.FileName = @"c:\windows\system32\cmd.exe";
p.StartInfo.Arguments = "/c dir c:\*.iso /s /b";
p.Start();
string output = p.StandardOutput.ReadToEnd();
p.WaitForExit();

After this you can split the output using \n

This is telling to search all ISO files in directory+all sub-directories and give only path+files names.

You can also use:

Directory.GetFiles(@"c:\", "*.iso", SearchOption.AllDirectories)

Change File Extension Using C#

There is: Path.ChangeExtension method. E.g.:

var result = Path.ChangeExtension(myffile, ".jpg");

In the case if you also want to physically change the extension, you could use File.Move method:

File.Move(myffile, Path.ChangeExtension(myffile, ".jpg"));

FileUpload get file extension

"Path" am I missing a using statement?

You have to add

using System.IO; 

to the list of namespaces

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