[Bug c++/114571] New: -Wzero-as-null-pointer-constant does not complain about NULL

[Bug c++/114571] New: -Wzero-as-null-pointer-constant does not complain about NULL

[ossman at cendio dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114571

            Bug ID: 114571
           Summary: -Wzero-as-null-pointer-constant does not complain
                    about NULL
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ossman at cendio dot se
  Target Milestone: ---

Created attachment 57857
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57857&action=edit
Test case

We are looking at bringing up the TigerVNC project to a more modern C++ style,
and one thing was using nullptr instead of NULL. We were very glad when we
found -Wzero-as-null-pointer-constant to help out with this.

Unfortunately, it doesn't seem to do much for NULL in modern¹ gcc. It spots
usage of "0", but not any "NULL". clang has no trouble finding both.

I've attached a test case with some comments on the cases we've seen.

¹ gcc 5 spots some, but not all NULL

[Bug c++/114571] -Wzero-as-null-pointer-constant does not complain about NULL

[ossman at cendio dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114571

--- Comment #1 from Pierre Ossman <ossman at cendio dot se> ---
Hmm.. I found bug 77513, and r9-873. So I guess this is intentional?

This makes the warning somewhat pointless. We want to make sure developers
standardise on nullptr, both for style and since the behaviour of NULL is
compiler dependent (if I'm understanding the C++ standard correctly).

It's also annoying if there is not a consensus between clang and gcc here.

[Bug c++/114571] -Wzero-as-null-pointer-constant does not complain about NULL

[ossman at cendio dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114571

--- Comment #2 from Pierre Ossman <ossman at cendio dot se> ---
Found another case that neither gcc 5, gcc 13, nor clang complain about for
some odd reason:

>  assert(thing == NULL);

All three complain about:

>  assert(thing == 0);

Not sure what's going on here.

[Bug c++/114571] -Wzero-as-null-pointer-constant does not complain about NULL

[ossman at cendio dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114571

--- Comment #3 from Pierre Ossman <ossman at cendio dot se> ---
And another odd case; gcc 5 complains about this:

> const char *a;
> a = NULL;

but not:

> const char *a = NULL;

gcc 13 complains about neither, and clang about both.