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In-Reply-To: <20050810093352.EAD8B5287F@svr1.postgresql.org>
References: <20050810093352.EAD8B5287F@svr1.postgresql.org>
Date: Wed, 10 Aug 2005 12:52:12 +0200 (CEST)
Subject: Re: Getting oid with libpq
From: jtv@xs4all.nl
To: "Johan C. de Koning" <johan.de.koning@geodan.nl>
Cc: pgsql-interfaces@postgresql.org
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Johan C. de Koning wrote:

> I have stored some large objects (which are images) with the lo_import
> function. Now I can read the images with the other functions like lo_read
> within libpq. But I have one problem with the oid I have to give to this
> method. Inside my program I will do a select like this

> Select texture from building_face where face_id > 100;

> Textures is the oid field. When I use PQgetValue() I get a complete
> different value then when I do  a select inside pgAdmin. How can I get the
> same oid so that I can use this for reading the data of the images inside
> my c++ program. Because it is not working with the oid from PQgetValue.

Just a guess, but...

One mistake many people make is to cast the char * returned by
PQgetValue() to the type they expect to get.  Which won't work, since it's
a pointer to a value (in this case a number) in a textual format.  It
needs to be parsed so you get the actual numeric value.

Also, when you parse the number, be aware that the standard-library
functions (such as sscanf()) take the applicable locale setting into
account--which is not what you want in this case.  Best reset to the
default locale before parsing.


Jeroen