User-Agent: Microsoft-Entourage/10.1.4.030702.0
Date: Wed, 29 Mar 2006 21:20:21 -0700
Subject: PQexecPrepared Problem with paramValues
From: Keary Suska <hierophant@pcisys.net>
To: Postgres-Interfaces <pgsql-interfaces@postgresql.org>
Message-ID: <C050AA95.27A69%hierophant@pcisys.net>
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To risk exposing my less-than-geek level knowledge of C, I am having a
problem with PQexecPrepared where it crashes every time.

I am pretty sure it is because I am not sending the right kind of pointer to
the paramValues. I am certain that the problem has to do with the parameter
in any case, because I can execute successfully with static values.

I know this is probably more of a C issue, but I hoping someone has the
heart to help.

Note: I am working in objective-C, and not in C, so I need to convert from
one data representation to one libpq understands. This may help explain why
the approach below is odd.

After a successful prepare, I calloc() a buffer like so:

char *buffer = calloc( 1, maxLen );

where maxLen is the total size of concatenated strings including terminating
nulls.

I then populate the buffer with the strings sequentially. This seems to be
working without any issues (I have verified).

I am assuming that this format is OK since the documentation doesn't
indicate that a proper two-dimensional array is required. Notwithstanding, I
need to work with an arbitrary number of parameters of arbitrary length.

But every way I have tried to pass the buffer (or some other variable made
into a compatible pointer type) causes a crash in the guts of libpq.

An example call:
pgResultStruct = PQexecPrepared( [connection pgConnStruct], "", params,
&buffer, NULL, NULL, 0 );

Of course, the compiler doesn't like the parameter in this case. Trying to
convert to a compatible pointer type:

  const char *buf2 = buffer;
  const char * const *paramValues = &buf2;
  pgResultStruct = PQexecPrepared( [connection pgConnStruct], "", params,
paramValues, NULL, NULL, 0 );

The compiler doesn't mind but libpq crashes.

This is probably a simple issue, but I can't seem to figure it out.

Best,

Keary Suska
Esoteritech, Inc.
"Demystifying technology for your home or business"