File output is not as expected - ms-access

Question

The following piece of code is giving unexpected results, but very rarely. It works about 99% of the time. It should be outputting an XML file.
Open XMLPath & dblFoo & ".xml" For Output As #15
Print #15, "<?xml version=" & Q & "1.0" & Q & " encoding=" & Q & "utf-8" & Q & "?>"
Print #15, "<main>"
Print #15, "<general>"
Print #15, "<foo>BAR</foo>"
Print #15, "</general>"
Print #15, "<foobar_entry>"
Print #15, "<bar_name>" & Replace(dblFoo, ".", "_") & "_" & someOtherVal & "_F0" & "</bar_name>"
`
` some more tag printing
`
Print #15, "</foobar_entry>"
Print #15, "</main>"
Close #15
Now, the 'bad part' of the output XML file will look like this:
</general>
try>
... rest of file looks normal
In this case the first part of <foobar_entry> has been cut off.
Another error it will show is:
</main>
NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL NUL
Where NUL is ASCII code 0.
Could garbage data be output to the file that would move the current read/write position in the file?
Is this just a matter of two people calling the function at the same time? It is an Access application after all, with many users on the system.
There doesn't seem be any error checking code when writing to the file or opening the file.

Answer 1

I strongly recommend not using Print if you want reliable output in files. Access's text mode printing is known to cause trouble, since it includes a lot of logic to do things like concatenating variables and writing non-text variables to CSV.
Instead, use binary writing to be in control of what actually gets written to the file.
Open XMLPath & dblFoo & ".xml" For Binary Access Write As #15
Put #15, , "<?xml version=" & Q & "1.0" & Q & " encoding=" & Q & "utf-8" & Q & "?>" & vbCrLf
Put #15, ,"<main>" & vbCrLf
'Etc
Close #15
Also note that this is low-level file IO, that means, each write statement is sent to the disk without buffering. I strongly recommend writing the whole string at once, and not using tons of little Print/Put statements. Else, performance will suffer, especially on network drives.
Note that you specify encoding=utf-8 in your XML file, but you're certainly not encoding it as UTF-8 if you're writing it to a file this way, though.