Detecting if a file is already open

  • Thread starter Thread starter CaptainCaveman
  • Start date Start date
C

CaptainCaveman

Hi

Is there a solid method for testing if a file is already open so I dont try
an open a file in use by another process?

TIA
 
I'm assuming from your post that you mean the old classic

try
{
}
catch(exception ex)
{
}
technique?

Is that really the only way?

TIA
 
I'm assuming from your post that you mean the old classic

try
{}

catch(exception ex)
{}

technique?

Is that really the only way?

TIA
Click to expand...

public bool FileIsLocked(string strFullFileName) {
bool blnReturn = false;
System.IO.FileStream fs;
try {
fs = System.IO.File.Open(strFullFileName,
IO.FileMode.OpenOrCreate, IO.FileAccess.Read, IO.FileShare.None);
fs.Close();
}
catch (System.IO.IOException ex) {
blnReturn = true;
}
return blnReturn;
}
 
Hi

Is there a solid method for testing if a file is already open so I dont try
an open a file in use by another process?

TIA
Click to expand...

the short answer is NO.

You have to try/catch the file operation.
 
I'm assuming from your post that you mean the old classic

try
{}

catch(exception ex)
{}

technique?

Is that really the only way?
Click to expand...

YES, there is no other way.
 
I have an app which needs this same thing. Here is the approach I take:

/// <summary>
/// Determines if a specific file is locked
/// </summary>
/// <param name="aFile">File to check for locking</param>
/// <returns>True if inuse; False if available</returns>
public static bool isFileLocked(string aFile)
{
try
{
if ((File.GetAttributes(aFile) & FileAttributes.ReadOnly) !=
FileAttributes.ReadOnly)
{

FileStream fs = new FileStream(aFile, FileMode.Open,
FileAccess.ReadWrite, FileShare.None);
try
{
fs.ReadByte();
}
catch
{
return true;
}
finally
{
fs.Close();
fs.Dispose();
}
}
}
catch
{
return true;
}
return false;
}
 
Ignacio said:
YES, there is no other way.
Click to expand...

You can P/Invoke CreateFile which will give an error number instead of
throwing an exception.

Don't forget to CloseHandle on success.
 
Ryan said:
I have an app which needs this same thing. Here is the approach I
take:
Click to expand...

I just want to point out that here returning false means "it wasn't locked
when I checked" not "it's unlocked and opening will now succeed". Handling
locking collisions CANNOT reliably be done using a separate isFileLocked
check, it has to be done atomically with opening the file for your own use.
 
CaptainCaveman said:
Hi

Is there a solid method for testing if a file is already open so I
dont try an open a file in use by another process?

TIA
Click to expand...

You need to go ahead and try to open the file, any test you can imagine will
return information that is already out-of-date (some program can lock the
file after your test said all is ok and you will still end up trying to open
a locked file).
 
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