What is the best way to test if a file is open

[sls@cnicorp.com]

I am using VS2005 VB and running into a problem that my program is processing files while they are still in use.

 

[JuggaloBrotha]

The only way to know if a file is open is to try to open it yourself with exclusive access. Look into the System.IO.StreamReader class and try to open your file with read-only exclusive access.

 

[jmcilhinney]

The only way to know if a file is open is to try to open it yourself with exclusive access. Look into the System.IO.StreamReader class and try to open your file with read-only exclusive access.

The principle is correct but don't use a StreamReader. A StreamReader is for reading text from a stream. If you don't want to read text then it serves no purpose. You may as well just create the stream directly because the StreamReader will create a FileStream under the hood anyway.

 

[cjard]

here's a scrap of C# I use for this very purpose:

    private bool FileInUse(string filename)
    {
      // If the file can be opened for exclusive access it means that the file    
      // is no longer locked by another process.    
      try {
        using (FileStream f = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.None)) {
          return false;
        }
      } catch (FileNotFoundException fnfe) {
        throw fnfe;
      } catch (IOException) {
        return true;
      }
    }

 

[JuggaloBrotha]

here's a scrap of C# I use for this very purpose:

    private bool FileInUse(string filename)
    {
      // If the file can be opened for exclusive access it means that the file    
      // is no longer locked by another process.    
      try {
        using (FileStream f = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.None)) {
          return false;
        }
      } catch (FileNotFoundException fnfe) {
        throw fnfe;
      } catch (IOException) {
        return true;
      }
    }

That works too, I simply suggest to people to use a StreamReader because usually they're already familiar with using it, and having open the file exclusively will still throw the exception if the file's in use.

 

[mrojas]

Function IsFileAvailable(ByVal theDocument As String) As Boolean
        Try
            File.Open(theDocument, FileMode.Open, FileAccess.ReadWrite, FileShare.None)
            IsFileAvailable = True
        Catch
            IsFileAvailable = False
            ' Display whatever message appropriate
        End Try
End Function

 

[JuggaloBrotha]

Since this thread's come back up, I might as well state this here too, checking to see if a file's in use before actually opening it to read/write it is pointless (and this actually happened to me once) in the split second between the file check and actual opening of the file for read/write another process could still open the file, which means it's not in use so it passes the check, then my write routine got an exception because the file was in use.

Your best bet is to just open the file and try to do whatever needs to be done because checking the file's availability first is pointless.