(This is yet another reason why I hate programming for Win32, even if only through CPAN.)

In DBM::Deep 0.98 and above, we added the feature that you could pass in your own filehandle instead of a filename. (This allows you to use the *DATA filehandle as a DBM::Deep file.) The only issue is that DBM::Deep opens its filehandles as read-write handles. Potentially, you could pass us a read-only filehandle. (I'm not even going to comment on the stupidity of passing a write-only filehandle to DBM::Deep.)

If you do, then accidentally try to modify the data, then a warning gets popped up in print() saying "Cannot print to a closed filehandle". Fatal doesn't work because print() cannot be overridden. While I could trap the warning, I'd still prefer to detect the fact that the filehandle isn't writable and throw an error.

I found the following code somewhere on Perlmonks (Thanks, Zaxo!) and it does the trick: 

sub _is_writable {
    my $fh = shift;
    (O_WRONLY | O_RDWR) & fcntl( $fh, F_GETFL, my $slush = 0);
}

[download]
The code works great . . . on systems whose Fcntl have defined F_GETFL. Unfortunately, that doesn't seem to include Win32 (at least not for ActiveState 5.8.6).

Other than disabling that function for Win32, how should I go about fixing this problem?

Update: Zaxo's code is found here

My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to F_GETFL and Win32 by dragonchild

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