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The Joel on Software Discussion Group (CLOSED)

How can I check if a text file is not already open (by a 3rd party application, not mine)

Is there a dos command that does that, or an API ?

I'm aware that there's some sysinternals tool that does it but I really need a function that I can call from our corporate ERP system

if %open(filename);
  // do something;
endif;

You weren't languange specific...

There is a utility available for UNIX-like operating systems called 'lsof' (list open files).

Will

you need to try to open it *exclusively*, failing that someone else has it open.

"you need to try to open it *exclusively*, failing that someone else has it open."

That's the correct approach, but be sure to check the error code (again, OS/language specific) to be sure that's why it failed.

As a rule, the correct way to find out whether you can do X with a file is to try to do it and check the result. Testing first and then trying to do it introduces a race condition. The state of the file can change between testing it and doing something with it, in the OP's case between checking for another reader and opening the file.

And just keep in mind... not all programs lock a file when they open it.  Notepad doesn't, and many text editors don't.

lsof is Linux specific.

To the O/P, get the book "Advanced Windows Programming", which describes how these things can be looked up. Unfortunately, I don't know enough to give an answer off the top of my head.

Most common reason to want to know if a file is open is to be sure a file copy is complete. Is that what's going on here?

http://msdn2.microsoft.com/en-us/library/aa363874.aspx