Two seperate problems with libpq - arrays and bytea edit

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 =
$1;",
np, NULL, paramValues, paramLen, NULL, 1);
if (PQresultStatus(r) != PGRES_COMMAND_OK) {
NSLog(@"UPDATE failed: %s", PQerrorMessage([conn conn]));
}
PQclear(r);

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];
PQfreemem(decoded);
}
}

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];
}