Hi all,

    I got strange result with PQgetisnull, say

for empty table(I think that it's empty so null)

I guess that
after fetch some selection
PQgetisnull(result, 0, 0) should give me "1 or true"
But
it gives me
ERROR! field 0(of 0) of row 0(of 0) is not available... Segmentation
Fault

so I tried
if (PQntuples(result) == 0)
...

But  PQntules gives me "1" not "0" !

do I have to check result with
char* value = PQgetvalue(result, 0, 0);
and test value is "" or not?  any idea???

I'm using v6.3.2 on linux && Solaris.

Best Regards, C.S.Park


Thu, 16 Jul 1998 17:10:43 +0900
"Park, Chul-Su" <pcs@mhlx01.kek.jp>
[BUG?] strange PQgetisnull
"Park, Chul-Su" <pcs@mhlx01.kek.jp> writes:
>     I got strange result with PQgetisnull, say
> for empty table(I think that it's empty so null)
> I guess that
> after fetch some selection
> PQgetisnull(result, 0, 0) should give me "1 or true"
> But
> it gives me
> ERROR! field 0(of 0) of row 0(of 0) is not available... Segmentation
> Fault

PQgetisnull is buggy in 6.3.2: it range-checks the tuple and field
numbers, and complains if they are out of range ... but then falls
through and tries to reference the tuple info anyway.  Thus, segfault.

It should return a default value (probably 1 to pretend the field is
NULL) when the indexes are out of range.  This is already fixed in the
current development sources, but if you want to stick with a 6.3.2
server then you will have to modify fe-exec.c yourself.

> so I tried
> if (PQntuples(result) == 0)
> ...
> But  PQntules gives me "1" not "0" !

The PQgetisnull error message you quoted above indicates (after looking
at the 6.3.2 sources) that nfields was 1 and ntuples was 0.  I think you
are testing the results of a different query here.

> do I have to check result with
> char* value = PQgetvalue(result, 0, 0);
> and test value is "" or not?  any idea???

No, you should be checking PQntuples and perhaps also PQnfields to be
sure that the indexes you are going to use are OK.

			regards, tom lane

Thu, 16 Jul 1998 10:11:23 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: [HACKERS] [BUG?] strange PQgetisnull 
> Hi all,
> 
>     I got strange result with PQgetisnull, say
> 
> for empty table(I think that it's empty so null)
> 
> I guess that
> after fetch some selection
> PQgetisnull(result, 0, 0) should give me "1 or true"
> But
> it gives me
> ERROR! field 0(of 0) of row 0(of 0) is not available... Segmentation
> Fault

You can't check for isnull on a Result that returns no rows.  It is only
for looking at fields of an existing returned row.

-- 
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maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
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Thu, 16 Jul 1998 11:27:11 -0400 (EDT)
Bruce Momjian <maillist@candle.pha.pa.us>
Re: [HACKERS] [BUG?] strange PQgetisnull