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* [musl] Re: [PATCH] Define NULL as nullptr when used in C++
@ 2021-12-23 19:13 Colin Cross
  2021-12-23 21:05 ` Rich Felker
  0 siblings, 1 reply; 4+ messages in thread
From: Colin Cross @ 2021-12-23 19:13 UTC (permalink / raw)
  To: musl; +Cc: Ismael Luceno

On Sun, Aug 15, 2021 at 05:51:57PM +0200, Ismael Luceno wrote:
> This should be safer for casting and more compatible with existing code
> bases that wrongly assume it must be defined as a pointer.

This seems to meet the C++ spec for NULL [1], but I noticed some
compatibility issues with code that was previously compiling with
glibc.

I've found multiple places that used reinterpret_cast<int*>(NULL),
which now fail with:
error: reinterpret_cast from 'nullptr_t' to 'int *' is not allowed
According to [2] those should technically be static_cast and not
reinterpret_cast.

I've also seen failures with returning NULL from a function with a
jlong return type:
error: cannot initialize return object of type 'jlong' (aka 'long')
with an rvalue of type 'nullptr_t'

glibc uses __null if __GNUG__ is set, ((void*)0) for __cplusplus, or 0 for C.

This also meets the C++ spec for NULL [1], but is an improvement over
the previous 0L because it can be correctly interpreted as a NULL
sentinel value by Clang's -Wsentinel warning.

Ismael, can you give an example of the code that assumes NULL is a
pointer?  Does it work with __null (assuming you're using a compiler
that has GNU extensions like __null)?

In any case, I'll fix the technically incorrect code I have access to
so that it works with nullptr.

[1] https://en.cppreference.com/w/cpp/types/NULL
[2] https://en.cppreference.com/w/cpp/language/reinterpret_cast

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-12-24  1:28 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-12-23 19:13 [musl] Re: [PATCH] Define NULL as nullptr when used in C++ Colin Cross
2021-12-23 21:05 ` Rich Felker
2021-12-23 22:01   ` Ismael Luceno
2021-12-24  1:28   ` Rich Felker

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