Thread: Why pfree(NULL) breaks execution?

C doesn't break on free(NULL) so why is pfree developed to break on NULL?<br />Is there any way in PostgreSQL to
overcomethis so that it won't break, apart from checking if the pointer NULL?<br /> 

On Fri, Mar 4, 2011 at 8:08 AM, Marios Vodas <mvodas@gmail.com> wrote:
> C doesn't break on free(NULL) so why is pfree developed to break on NULL?
> Is there any way in PostgreSQL to overcome this so that it won't break,
> apart from checking if the pointer NULL?

I think that free(NULL) works on some platforms but not all.  I don't
see what advantage we'd get out of making pfree(NULL) silently work,
and there's a clear disadvantage: it would remove a useful sanity
check.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

On 4 March 2011 14:50, Robert Haas <robertmhaas@gmail.com> wrote:
> I think that free(NULL) works on some platforms but not all.  I don't
> see what advantage we'd get out of making pfree(NULL) silently work,
> and there's a clear disadvantage: it would remove a useful sanity
> check.

I don't feel particularly strongly about what pfree() should do one
way or the other, but that isn't so; free(NULL) works on all
platforms, and is required to by the standard.

--
Regards,
Peter Geoghegan

Peter Geoghegan <peter.geoghegan86@gmail.com> writes:
> On 4 March 2011 14:50, Robert Haas <robertmhaas@gmail.com> wrote:
>> I think that free(NULL) works on some platforms but not all. �I don't
>> see what advantage we'd get out of making pfree(NULL) silently work,
>> and there's a clear disadvantage: it would remove a useful sanity
>> check.

> I don't feel particularly strongly about what pfree() should do one
> way or the other, but that isn't so; free(NULL) works on all
> platforms, and is required to by the standard.

For the last few years it's been pretty safe to assume that, but it did
not use to be so --- pre ISO C spec, some malloc libraries allowed
free(NULL) and some didn't.

In any case, this has been debated before and the project policy is
that having pfree(NULL) throw an error is a net benefit.  The main case
where it's really useful to not throw an error is where malloc(0)
returns NULL rather than a valid pointer (and BTW, both of those
behaviors are allowed by spec).  However, palloc(0) is guaranteed
to give you a valid pointer that you can pfree, so that argument
doesn't hold here.
        regards, tom lane