How to get full path of StreamWriter

Question

I'm creating a StreamWriter using a relative path. But the file doesn't appear. To troubleshoot, I want to check that the full path is what I'm expecting. So having a StreamWriter instance, how can I get the full path of the file it's going to write to?

string fileName = "relative/path.txt"
StreamWriter sw= new StreamWriter(fileName);
// What is the full path of 'sw'?

Have you considered that when you run your application inside visual studio the current directory is bin/debug or bin/release ? — Steve, May 07 '12 at 13:54
@Steve yes i'm looking for files in bin/debug/release directory.... files are not there and that's why I want to obtain full path programatically. To compare if i'm searching in the right dir — Oleg Vazhnev, May 07 '12 at 13:55
ok I've used "search files" feature of Windows and finally found where my files are. question can be closed or can be left opened so someone can answer it... — Oleg Vazhnev, May 07 '12 at 13:57
@javapowered If this file can be closed, that you can do this on yourself. — Oliver, May 07 '12 at 14:12

score 65 · Answer 1 · edited Jul 25 '19 at 19:54

65

In my version of the framework, this seems to work:

string fullPath = ((FileStream)(streamWriter.BaseStream)).Name;

(Found by debugging.)

edited Jul 25 '19 at 19:54

spottedmahn

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answered May 07 '12 at 14:03

Jeppe Stig Nielsen

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4

Exactly the kind of answer that suits the question-title. Did you mean found by `introspection`...? – Lorenz Lo Sauer Sep 14 '13 at 06:25

score 11 · Accepted Answer · edited Dec 02 '14 at 22:37

11

To get the full path from a relative path, use the Path.GetFullPath method.

For example:

string fileName = "relative/path.txt";
string fullPath = Path.GetFullPath(fileName);

edited Dec 02 '14 at 22:37

Peter Mortensen

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answered May 07 '12 at 13:57

Steve

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score 1 · Answer 3 · answered May 07 '12 at 13:59

Might be the directory 'relative' not exists. Either create it manually. Or create it programmatically as below

string fileName = @"relative\path.txt";
fileName = Path.GetFullPath(fileName);
Directory.CreateDirectory(Path.GetDirectoryName(fileName));

StreamWriter sw= new StreamWriter(fileName, true);

score 0 · Answer 4 · answered Jan 29 '19 at 13:17

0

Dim fs As FileStream = CType(sw.BaseStream, FileStream)
Dim fi As New FileInfo(fs.Name)
Console.WriteLine(fi.FullName)

answered Jan 29 '19 at 13:17

Aave

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score 0 · Answer 5 · answered Dec 16 '20 at 21:59

0

This would be better as a comment to @Jeppe Stiehl Nielsen's reply, but I can't add comments: In VB.Net, this becomes:

Dim fullPath As String = CType(streamWriter.BaseStream, FileStream).Name

I'm not sure why the CType is needed, and only for this property while all other properties do not, but it's needed.

answered Dec 16 '20 at 21:59

CeSinge

21
6

Because `CType` casts an object's type. `BaseStream` is a `Stream`. `FileStream` inherits that base class, but in this case we're sure that the base stream is actually a file stream because that's what the path points to. Ie. the path is not a stream to a FTP connection for example. – Paul-Sebastian Manole Jul 10 '21 at 22:58

score 0 · Answer 6 · answered Jul 10 '21 at 23:15

Using nullable types and safe casting (as doesn't throw exceptions):

_logger.LogInformation("Wrote file at {0}", (streamWriter.BaseStream as FileStream)?.Name);

? only accesses the property if the result of the expression on the left is not null, otherwise it returns (evaluates to) null (it's like it's equivalent to E is T ? (T)(E) : (T)null).

If you wanted, you could check the cast result for null like this:

var fs = streamWriter.BaseStream as FileStream;

if (fs != null)
{
    _logger.LogInformation("Wrote file at {0}", fs.Name);
}

But that's more code than you need. The more modern way to write the above example with C# 7+ is to use the is operator:

if (streamWriter.BaseStream is FileStream fs)
{
    _logger.LogInformation("Wrote report file at {0}", fs.Name);
}

This has the added benefit that the log call doesn't happen at all, if the cast could not be performed, because actually fs is never null when using is. The entire is expression evaluates to either true or false, but never null.

Serj-Tm · Answer 7 · 2012-05-07T18:29:57.587

  var fstream = sw.BaseStream as System.IO.FileStream;
  if (fstream != null)
    Console.WriteLine(GetAbsolutePathByHandle(fstream.SafeFileHandle));


[DllImport("ntdll.dll", CharSet = CharSet.Auto)]
private static extern int NtQueryObject(SafeFileHandle handle, int objectInformationClass, IntPtr buffer,  int StructSize, out int returnLength);

static string GetAbsolutePathByHandle(SafeFileHandle handle)
{
  var size = 1024;
  var buffer = Marshal.AllocCoTaskMem(size);
  try
  {
    int retSize;
    var res = NtQueryObject(handle, 1, buffer, size, out retSize);
    if (res == -1073741820)
    {
      Marshal.FreeCoTaskMem(buffer);
      size = retSize;
      Marshal.AllocCoTaskMem(size);
      res = NtQueryObject(handle, 1, buffer, size, out retSize);
    }
    if (res != 0)
      throw new Exception(res.ToString());
    var builder = new StringBuilder();
    for (int i = 4 + (Environment.Is64BitProcess ? 12 : 4); i < retSize - 2; i += 2)
    {
      builder.Append((char)Marshal.ReadInt16(buffer, i));
    }
    return builder.ToString();
  }
  finally
  {
    Marshal.FreeCoTaskMem(buffer);
  }
}

Output:

\Device\HarddiskVolume2\bla-bla\relative\path.txt

How to get full path of StreamWriter

7 Answers7