VB Forum / General 2 / September 2004

There are several things to consider with this. If it is some kind of log
file, it should remain open to minimise the system resources being used by
the log file (although it uses a file handle continuously, it would be in
use fairly often anyway and opening and closing takes time + memory).
However if it is a shared/communication file between two concurrent programs
you should open and close it each time to keep it clean (I'd make a
WriteDataToFile function to make it easier to).

It also depends on how many other files you are using in your program and
how you get their file numbers. You can statically assign each file a
specific number, or use the FreeFile function, each method having its own
advantages and disadvantages. Basically static is good for when there are a
fixed number of files used by your program (log file, INI file, user data
file, backup data file), whereas using FreeFile is better if you are making
a program where there are going to be a random number of files open (like a
word processing program). If you are making a program with a random number
of open files I would suggest not using static numbering even for the
constantly open files (log files, etc) as if an error occurs and you need to
close then open the file, in the mean time the user could have opened
another file and used that file number.

Bottom line is do it whatever way you would find easier to code. If you
really want the optimum code for your program then the best thing would be
to try it both ways and measure the CPU and memory usage while the program
is running. If your running windows XP this is REALLY easy. Just open the
task manager and go into the Processes tab. Open up Visual Basic from
scratch and start running your program. Then take a note of the CPU time and
Peak Mem Usage fields in the table there for visual basic (or your program
depending on the version of visual basic).

Hope this helps.

Opening files is time consuming
- there is a very substantial 'hit' on opening files.

However if a file has been updated and will not be re-used in the next
few seconds, I always close the file and re-open it to ensure that the
data really hits the disk.

One system crash with a partially updated open file wipes out any
speed gains.

I also pre-extend files if possible before writing the data, then
close them and re-open them to ensure that the Directory info matches
that in the FAT