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Re: Determining C type for a given OID

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Graham Wilson <grahamwilsonca(at)yahoo(dot)ca>
Cc: pgsql-interfaces(at)postgresql(dot)org
Subject: Re: Determining C type for a given OID
Date: 2002-11-29 23:34:07
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-interfaces
Graham Wilson wrote:
> Hi all,
> I'm using the libpq `PQgetvalue` function to get
> specific results from my datase.  Many of these
> results are numeric types.  Is there an internal
> function in libpq that will convert the returned
> string to an appropriate C-type based on the oid
> values in src/include/catalog/pg_type.h?

Well, in most queries, the returned value is a C string that you have
to convert in the client.  I think ecpg handles such conversions
natively so you don't have to worry about them, and most of the
scripting languages handle a C string numeric value just like any other
value (they don't have data types).  It would be great if we could
assign it right to a double, but you can't.

You can make such assignments of float4 to float and float8 to double if
you use a binary cursor _and_ your client and server have the same
internal representation for such values. However, NUMERIC is stored
internally a binary-coded decimal-like format that isn't going to make
any sense to your client code at all.

  Bruce Momjian                        |
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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