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Message-ID: <3A36A9A8.AE148FE0@ece.gatech.edu>
Date: Tue, 12 Dec 2000 17:41:44 -0500
From: Charles Wilson <cwilson AT ece DOT gatech DOT edu>
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To: Jeff Lu <jklcom AT mindspring DOT com>
CC: cygwin AT cygwin DOT com
Subject: Re: Need some helps on using dbm functions
References: <NDBBIHPECLIGKCCLMACAGEHBCIAA DOT jklcom AT mindspring DOT com>
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Jeff Lu wrote:
> 
> I've a small program that writes data using dbm calls
> 
> here's a snapshot of code and how I compile it:
> gcc -s -o /e/inetpub/wwwroot/cgi-bin/send.exe send.c
> intrautil.c -DBM_STATIC -lgdbm

The readme /usr/doc/Cygwin/gdbm-1.8.0.README clearly states that you
must use "-DGDBM_STATIC" not "-DBM_STATIC" or some variant thereof.

I sent a more explanatory answer but it appears that the mail server
swallowed it.  I will repeat that explanation here, but don't be
surprised if the mailserver eventually disgorges the previous one and
you see another message like this one.

> When the program is run, info.pag gets created but dbm_open returns a NULL
> file handle dbm_local.  In Unix there is info.dir file that goes with
> info.pag but I don't see one here in cygwin.  Is this the way it's supposed
> to be?  Can some one tell me why this is happening?  thanks.

Normal ndbm databases consist of two files: foo.dir and foo.pag.  gdbm
databases consist of a single file "foo".  When you use gdbm in its
"ndbm emulation" to create a new "ndbm"-style database (e.g. by calling
'dbm_open("my non-existant database")'  -- remember that 'dbm_open' is
an ndbm-style entry point; true gdbm programs use 'gdbm_open') it first
creates a gdbm-style database with the name "foo.pag". Then, it
HARDLINKS the file "foo.dir" to that new foo.pag database.

From that point on it only accesses foo.pag.  However, the initial
creation step fails on FAT drives and under Win9x -- because Win9X only
supports FAT -- and hardlinks don't work on FAT drives.  (No, we can't
rewrite gdbm to use symlinks -- the hardlink is used to insure that the
timestamps on both files are the same; symlinks do not inherit the
timestamp of their target.)

So, the short answer is: ndbm-emulation doesn't work on Win9x or FAT. 
Are you using either of those?

--Chuck

P.S. Note that the comments in the source file gdbm-1.8.0/dbm_open.c are
wrong.  It states "NOTE: the file foo.dir is ignored and will always
have a size 0." That is incorrect, as inspection of the source code
itself will show.  I based my explanation above on the source code, not
the (wrong) comments.

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