Horton

Re: Pointer subtraction with a null pointer

Isaac Morland <isaac.morland@gmail.com>

View thread View on postgr.es
From: Isaac Morland <isaac.morland@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>, Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@gmail.com>
Date: 2022-03-26T16:34:10Z
Lists: pgsql-hackers 
On Sat, 26 Mar 2022 at 12:24, Andres Freund <andres@anarazel.de> wrote:


> NULL can never be part of the same "array object" or one past past the last
> element as the pointer it is subtracted from. Hence the undefined beaviour.
>

Even more fundamentally, NULL is not 0 in any ordinary mathematical sense,
even though it can be written 0 in source code and is often (but not
always) represented in memory as an all-0s bit pattern. I'm not at all
surprised to learn that arithmetic involving NULL is undefined.

Commits

  1. Suppress compiler warning in relptr_store().