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Re: allowing multiple PQclear() calls

From: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
To: Marko Kreen <markokr(at)gmail(dot)com>
Cc: Boszormenyi Zoltan <zb(at)cybertec(dot)at>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Josh Kupershmidt <schmiddy(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: allowing multiple PQclear() calls
Date: 2013-01-02 15:52:36
Message-ID: 50E457C4.40709@vmware.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 02.01.2013 17:27, Marko Kreen wrote:
> On Wed, Jan 2, 2013 at 5:11 PM, Boszormenyi Zoltan<zb(at)cybertec(dot)at>  wrote:
>> 2012-12-11 16:09 keltezéssel, Simon Riggs írta:
>>
>>> On 11 December 2012 12:18, Boszormenyi Zoltan<zb(at)cybertec(dot)at>  wrote:
>>>
>>>>>> Such mechanism already exist - you just need to set
>>>>>> your PGresult pointer to NULL after each PQclear().
>>>>>
>>>>> So why doesn't PQclear() do that?
>>>>
>>>>
>>>> Because then PQclear() would need a ** not a *. Do you want its
>>>> interface changed for 9.3 and break compatibility with previous versions?
>>>
>>> No, but we should introduce a new public API call that is safer,
>>> otherwise we get people continually re-inventing new private APIs that
>>> Do the Right Thing, as the two other respondents have shown.
>>>
>>
>> How about these macros?
>
> * Use do { } while (0) around the macros to get proper statement behaviour.
> * The if() is not needed, both PQclear and PQfinish do it internally.
> * Docs
>
> Should the names show somehow that they are macros?
> Or is it enough that it's mentioned in documentation?

IMHO this doesn't belong into libpq, the interface is fine as it is. 
It's the caller's responsibility to set the pointer to NULL after 
PQclear(), same as it's the caller's responsibility to set a pointer to 
NULL after calling free(), or to set the fd variable to -1 after calling 
close(fd). There's plenty of precedence for this pattern, and it 
shouldn't surprise any programmer.

- Heikki


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Subject: Re: allowing multiple PQclear() calls
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