To: "Robert A. Knop Jr." <rknop@lilys.lbl.gov>
cc: pgsql-interfaces@postgresql.org
Subject: Re: 
In-reply-to: <Pine.LNX.4.10.10006301048490.30121-100000@milano.lbl.gov> 
References: <Pine.LNX.4.10.10006301048490.30121-100000@milano.lbl.gov>
Comments: In-reply-to "Robert A. Knop Jr." <rknop@lilys.lbl.gov>
	message dated "Fri, 30 Jun 2000 10:59:07 -0700"
Date: Fri, 30 Jun 2000 14:20:28 -0400
Message-ID: <19918.962389228@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Robert A. Knop Jr." <rknop@lilys.lbl.gov> writes:
>>>> No.  Unless the doc for the function explicitly says you should free
>>>> its result, it's a pointer into libpq-managed space.
>> 
>> Experience contradicts this.
>> I rewrote the thing explicitly freeing everything I got back from
>> PQfname() and PQgetvalue().  The memory leak was gone, and I didn't get
>> any segfaults or crashes.

I don't understand how.  In recent versions, not only is the pointer
you get back not a freshly-malloced chunk, it's not a malloc chunk at
all, but a pointer into the middle of a much larger malloc chunk.
You must have an extremely forgiving malloc library, one wherein free()
doesn't crash if handed a pointer that doesn't point at a malloc chunk.


>> Is there a Postgres developer who can confirm this one way or the other?

I am a Postgres developer, and if you don't want to take my word for it,
read the source code.  src/interfaces/libpq/fe-exec.c sez:

char *
PQgetvalue(const PGresult *res, int tup_num, int field_num)
{
    if (!check_tuple_field_number("PQgetvalue", res, tup_num, field_num))
        return NULL;
    return res->tuples[tup_num][field_num].value;
}

char *
PQfname(const PGresult *res, int field_num)
{
    if (!check_field_number("PQfname", res, field_num))
        return NULL;
    if (res->attDescs)
        return res->attDescs[field_num].name;
    else
        return NULL;
}

Actual loading of the PGresult structure is elsewhere in the same file,
but you can certainly see that you're not getting your very own copy
back here.

			regards, tom lane