Skip site navigation (1) Skip section navigation (2)

Two seperate problems with libpq - arrays and bytea edit

From: Teunis Peters <teunis(at)wintersgift(dot)com>
To: pgsql-interfaces(at)postgresql(dot)org
Subject: Two seperate problems with libpq - arrays and bytea edit
Date: 2005-05-14 18:40:10
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-interfaces
I'm trying to figure out how to read from and write to bytea values and 
array (specifically "text[2][]" for a key:value 'dictionary') and 
cannot figure it out.   Arrays I'm completely lost - I haven't a clue 
what the format would be.
bytea - my code segmentation faults.  PQgetlength returns 0.   I don't 
know if I'm putting it in the database correctly.

some sample code.  Yes it's in Objective C.   [db_result] embeds a 
"PGresult" value and does a lot of error checking.  image is of type 
NSData which basically holds binary data.  The rest SHOULD be clear.
I'd provide a smaller example except I'm not yet sure how to create 
console apps in MacOSX...   I suppose I could do it in linux though.

Any advice helpful.   I've been stewing my brain on this for a while 
now and am on something of a time limit.

getValue == PQgetvalue(res,tupple,field)
getlength == PQgetlength(res,tupple,field)
I hope that helps.

commit (subset of full code)
	sprintf(buf, "%i", cat_id);
	paramValues[np] = buf;           paramLen[np] = strlen(buf);    np++;
	paramValues[np] = [image bytes]; paramLen[np] = [image length]; np++;
	PGresult* r;
	r = PQexecParams([conn conn], "UPDATE images SET image = $2 WHERE id = 
					 np, NULL, paramValues, paramLen, NULL, 1);
	if (PQresultStatus(r) != PGRES_COMMAND_OK) {
		NSLog(@"UPDATE failed: %s", PQerrorMessage([conn conn]));

access (subset of full code)

	sprintf(buf, "%i", cat_id);
	paramValues[0] = buf;
	res = [db_result alloc];
	[res init:PQexecParams([conn conn], "SELECT image FROM images WHERE id 
= $1",1,NULL,paramValues,NULL,NULL,1)];
	if (!res) return nil;
	if ([res ntuples] < 1) return nil;
		char*     ptr;
		char*     decoded;
		size_t    i, decodedlen;
		NSString* ns;
		ptr = [res getValue:0 field:0];
		if (ptr != NULL) {
			i   = [res getlength:0 field:0];
			decoded = PQunescapeBytea(ptr, &decodedlen);
			image = [[NSData dataWithBytes:decoded length:decodedlen] retain];

Do I access bytea ("image" is a bytea type) this way, or this way:
		ptr = [res getValue:0 field:0];
		if (ptr != NULL) {
			i   = [res getlength:0 field:0];
			image = [[NSData dataWithBytes:decoded length:i] retain];


pgsql-interfaces by date

Next:From: Tom LaneDate: 2005-05-14 18:51:13
Subject: Re: Two seperate problems with libpq - arrays and bytea edit
Previous:From: Bruce MomjianDate: 2005-05-13 18:23:31
Subject: Re: bcc32.mak for libpq broken? (distro 8.0.0)

Privacy Policy | About PostgreSQL
Copyright © 1996-2017 The PostgreSQL Global Development Group