PQfmod and varchars

Hi list,

I'm trying to find out, from a client, how many characters will fit in a
varchar field
(http://pgfoundry.org/tracker/index.php?func=detail&aid=1000286&group_id=1000085&atid=394)
Problem is that when I do "PQfmod" on a varchar field defined as
"varchar(20)", PQfmod returns "24".

Now, it's fairly easy for me to subtract 4 from each result I get from
PQfmod, but I have a suspicion that this "4" is actually "pointer's
length", which means that I need to detect a 64 bit server and subtract
8 instead.

1. Is this suspicion correct?
2. If so, how do I detect how much to subtract.
3. If not, what is the meaning of "4"?

Thanks,
Shachar

--
Shachar Shemesh
Lingnu Open Source Consulting ltd.
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