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Re: libpq on windows

From: Gustavo Lopes <contratempo(at)gmail(dot)com>
To: pgsql-interfaces(at)postgresql(dot)org
Subject: Re: libpq on windows
Date: 2005-05-20 13:20:58
Message-ID: 2b5c484b05052006206c301de@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-interfaces
No, I'd say the notice processor/receiver is not the problem since
I've been able to implement a notice receiver that would display the
received notices without any complications.
The problem seems to arise only when a message contains a HINT
attached (I don't even know whether messages of type NOTICE can
cointain a hint field, but anyway that doesn't seem relevant to this
issue).

Gustavio Lopes

On 20/05/05, jtv(at)xs4all(dot)nl <jtv(at)xs4all(dot)nl> wrote:
> Gustavo Lopes <contratempo(at)gmail(dot)com> wrote:
> 
> > The problem seems to occurr only when the server sends a hint or the
> > dll generates one. This can happen when the connection to the server
> > cannot be established because the server is not running, a nonexistant
> > postgres function exist is called, when one attempts to drop an index
> > upon which a constraint depends, etc. (the program doesn't go beyond
> > PQconnectdb, PQexec or PQexecparam). Since my debugging skills are
> > very poor I cannot give any accurate description on what is causing
> > the exception.
> > The problem can be very easily reproduced by creating a C program
> > which calls PQconnectdb with a host parameter that points to a machine
> > that is not running postgres.
> > Running the same program under linux (although I used older versions
> > of the interface and the server) does not cause any problems.
> 
> It could be the notice processor that crashes.  A "notice processor" is a
> callback that you can register with libpq that handles error messages.
> The default is to print them to the console, but I'm not sure you can
> always do that in a Windows program.  Or since you're apparently using
> different compilers for libpq and the application, maybe the default
> notice processor gets linked to a different standard library than it
> expects and fails because of that.
> 
> Notice processors are documented here:
> 
> http://www.postgresql.org/docs/8.0/interactive/libpq-notice-processing.html
> 
> To find out if this is what's wrong, try creating an empty function (with
> C-style calling convention, not a regular C++ function) and setting that
> as the notice processor:
> 
>   extern "C" { /* (this line only needed in C++) */
>   void emptynoticeprocessor(void *, const char *)
>   {
>   }
>   } /* (this line only needed in C++) */
> 
> Now in your code, just after you opened your connection (call it "c"):
> 
>   PQsetNoticeProcessor(c,emptynoticeprocessor,NULL);
> 
> Of course that will mean that error messages are not displayed, so if this
> solves your crashing problem then your next step is to implement something
> here that displays the given message!
> 
> Jeroen
> 
>

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