How do I automatically delete tempfiles in c#?

Question

What are a good way to ensure that a tempfile is deleted if my application closes or crashes? Ideally I would like to obtain a tempfile, use it and then forget about it.

Answer 1

I use a more reliable solution:

using System.IO;
using System.Reflection;

namespace Konard.Helpers
{
    public static partial class TemporaryFiles
    {
        private const string UserFilesListFilenamePrefix = ".used-temporary-files.txt";
        static private readonly object UsedFilesListLock = new object();

        private static string GetUsedFilesListFilename()
        {
            return Assembly.GetEntryAssembly().Location + UserFilesListFilenamePrefix;
        }

        private static void AddToUsedFilesList(string filename)
        {
            lock (UsedFilesListLock)
            {
                using (var writer = File.AppendText(GetUsedFilesListFilename()))
                    writer.WriteLine(filename);
            }
        }

        public static string UseNew()
        {
            var filename = Path.GetTempFileName();
            AddToUsedFilesList(filename);
            return filename;
        }

        public static void DeleteAllPreviouslyUsed()
        {
            lock (UsedFilesListLock)
            {
                var usedFilesListFilename = GetUsedFilesListFilename();

                if (!File.Exists(usedFilesListFilename))
                    return;

                using (var listFile = File.Open(usedFilesListFilename, FileMode.Open))
                {
                    using (var reader = new StreamReader(listFile))
                    {
                        string tempFileToDelete;
                        while ((tempFileToDelete = reader.ReadLine()) != null)
                        {
                            if (File.Exists(tempFileToDelete))
                                File.Delete(tempFileToDelete);
                        }
                    }
                }

                // Clean up
                using (File.Open(usedFilesListFilename, FileMode.Truncate)) { }
            }
        }
    }
}

Every time you need temporary file use:

var tempFile = TemporaryFiles.UseNew();

To be sure all temporary files are deleted after application closes or crashes put

TemporaryFiles.DeleteAllPreviouslyUsed();

at start of the application.

Answer 2

Its nice to see that you want to be responsible, but if the files aren't huge (>50MB) you would be in line with everyone (MS included) in leaving them in the temp directory. Disk space is abundant.

As csl posted, the GetTempPath is the way to go. Users who are short on space will be able to run disk cleanup and your files (along with everyone else's) will be cleaned up.

Answer 3

I'm not primarily a C# programmer, but in C++ I'd use RAII for this. There are some hints on using RAII-like behaviour in C# online, but most seem to use the finalizer — which is not deterministic.

I think there are some Windows SDK functions to create temporary files, but don't know if they are automatically deleted on program termination. There is the GetTempPath function, but files there are only deleted when you log out or restart, IIRC.

P.S. The C# destructor documentation says you can and should release resources there, which I find a bit odd. If so, you could simply delete the tempfile in the destructor, but again, this might not be completely deterministic.