On Fri, May 09, 2025 at 10:31:38AM +0800, LIU Hao wrote:
> 在 2025-5-4 22:24, наб 写道:
> > Consider the following program, reduced from Lensfun:
> > #include <cstring>
> > extern char *f(const char *first_element, ...)
> > __attribute__((__sentinel__));
> > static auto N = f("a", "b", NULL);
> > static auto n = f("a", "b", nullptr);
> > static auto z = f("a", "b", 0);
> > #define NULL 123
> > in C++11 and later, NULL=nullptr so N/n are valid, and z is wrong.
>
> In C++ it's common to have `NULL` defined as `0`.
This is not the case. I think I was a little overzealous to say that
"C++11 <=> NULL=nullptr" (both C and C++ allow any "null-pointer constant"),
but both GCC and Clang define it as __null.
GCC:
77395be63213 (Richard Stallman 1992-03-30 02:25:19 +0000 413) #if defined
(_STDDEF_H) || defined (__need_NULL)
301264e6e9f7 (Michael Meissner 1991-11-27 20:06:32 +0000 414) #undef NULL
/* in case <stdio.h> has defined it. */
7a389b48df6a (Jason Merrill 1996-08-08 01:45:02 +0000 415) #ifdef __GNUG__
7a389b48df6a (Jason Merrill 1996-08-08 01:45:02 +0000 416) #define NULL
__null
7a389b48df6a (Jason Merrill 1996-08-08 01:45:02 +0000 417) #else /* G++
*/
be78ffb2267d (Jason Merrill 2000-06-24 18:19:46 -0400 418) #ifndef
__cplusplus
301264e6e9f7 (Michael Meissner 1991-11-27 20:06:32 +0000 419) #define NULL
((void *)0)
be78ffb2267d (Jason Merrill 2000-06-24 18:19:46 -0400 420) #else /* C++
*/
be78ffb2267d (Jason Merrill 2000-06-24 18:19:46 -0400 421) #define NULL 0
be78ffb2267d (Jason Merrill 2000-06-24 18:19:46 -0400 422) #endif /* C++
*/
7a389b48df6a (Jason Merrill 1996-08-08 01:45:02 +0000 423) #endif /* G++
*/
77395be63213 (Richard Stallman 1992-03-30 02:25:19 +0000 424) #endif /*
NULL not defined and <stddef.h> or need NULL. */
77395be63213 (Richard Stallman 1992-03-30 02:25:19 +0000 425) #undef
__need_NULL
$ git show 7a389b48df6a
commit 7a389b48df6a1622eb12ad09d5def385f357734b
Author: Jason Merrill <merr...@gnu.org>
Date: Thu Aug 8 01:45:02 1996 +0000
(NULL): Use __null for G++.
From-SVN: r12601
diff --git a/gcc/ginclude/stddef.h b/gcc/ginclude/stddef.h
index 49c2556e001..0cea45972da 100644
--- a/gcc/ginclude/stddef.h
+++ b/gcc/ginclude/stddef.h
@@ -306,7 +306,11 @@ typedef __WINT_TYPE__ wint_t;
#if defined (_STDDEF_H) || defined (__need_NULL)
#undef NULL /* in case <stdio.h> has defined it. */
+#ifdef __GNUG__
+#define NULL __null
+#else /* G++ */
#define NULL ((void *)0)
+#endif /* G++ */
#endif /* NULL not defined and <stddef.h> or need NULL. */
#undef __need_NULL
Clang:
272bcf6768d3c (Nico Weber 2014-04-30 04:35:09 +0000 102) #if
defined(__need_NULL)
0a4a8326c1027 (Ted Kremenek 2010-03-08 23:23:45 +0000 103) #undef NULL
95aa0b77f25c8 (Argyrios Kyrtzidis 2013-03-27 21:22:45 +0000 104) #ifdef
__cplusplus
1d725ecf93037 (Nico Weber 2012-04-24 21:27:01 +0000 105) # if
!defined(__MINGW32__) && !defined(_MSC_VER)
1d725ecf93037 (Nico Weber 2012-04-24 21:27:01 +0000 106) # define
NULL __null
1d725ecf93037 (Nico Weber 2012-04-24 21:27:01 +0000 107) # else
1d725ecf93037 (Nico Weber 2012-04-24 21:27:01 +0000 108) # define
NULL 0
1d725ecf93037 (Nico Weber 2012-04-24 21:27:01 +0000 109) # endif
6b0dc8511964e (Anders Carlsson 2008-11-04 06:53:14 +0000 110) #else
1d725ecf93037 (Nico Weber 2012-04-24 21:27:01 +0000 111) # define
NULL ((void*)0)
6b0dc8511964e (Anders Carlsson 2008-11-04 06:53:14 +0000 112) #endif
72da678d8c84c (Ian Anderson 2023-08-11 14:38:13 -0700 113) #undef
__need_NULL
72da678d8c84c (Ian Anderson 2023-08-11 14:38:13 -0700 114) #endif /*
defined(__need_NULL) */
commit 1d725ecf93037e8877286f53a7289f39064a9fc5
Author: Nico Weber <tha...@chromium.org>
Date: Tue Apr 24 21:27:01 2012 +0000
Let NULL and MSVC headers coexist better.
Fixes the two issues mentioned in PR12146.
llvm-svn: 155490
diff --git a/clang/lib/Headers/stddef.h b/clang/lib/Headers/stddef.h
index 9e87ee89b3b9..d7db826e676e 100644
--- a/clang/lib/Headers/stddef.h
+++ b/clang/lib/Headers/stddef.h
@@ -43,10 +43,13 @@ typedef __WCHAR_TYPE__ wchar_t;
#undef NULL
#ifdef __cplusplus
-#undef __null // VC++ hack.
-#define NULL __null
+# if !defined(__MINGW32__) && !defined(_MSC_VER)
+# define NULL __null
+# else
+# define NULL 0
+# endif
#else
-#define NULL ((void*)0)
+# define NULL ((void*)0)
#endif
#define offsetof(t, d) __builtin_offsetof(t, d)
0a4a8326c1027 (Ted Kremenek 2010-03-08 23:23:45 +0000 44) #undef NULL
6b0dc8511964e (Anders Carlsson 2008-11-04 06:53:14 +0000 45) #ifdef
__cplusplus
38321174e09cd (Chris Lattner 2010-08-03 22:13:56 +0000 46) #undef __null
// VC++ hack.
f7ab50df29066 (Douglas Gregor 2008-12-01 17:20:57 +0000 47) #define NULL
__null
6b0dc8511964e (Anders Carlsson 2008-11-04 06:53:14 +0000 48) #else
9e9b046ac95c9 (Eli Friedman 2008-05-20 13:34:26 +0000 49) #define NULL
((void*)0)
6b0dc8511964e (Anders Carlsson 2008-11-04 06:53:14 +0000 50) #endif
$ git show f7ab50df29066
commit f7ab50df290663597d02b8a5668866bfb57fc989
Author: Douglas Gregor <dgre...@apple.com>
Date: Mon Dec 1 17:20:57 2008 +0000
Define NULL to __null in C++, so that it's guaranteed to have the same
size as a pointer
llvm-svn: 60355
diff --git a/clang/lib/Headers/stddef.h b/clang/lib/Headers/stddef.h
index d5f4eb9c7c29..2c84b4b066c9 100644
--- a/clang/lib/Headers/stddef.h
+++ b/clang/lib/Headers/stddef.h
@@ -33,7 +33,7 @@ typedef __typeof__(*L"") wchar_t;
#endif
#ifdef __cplusplus
-#define NULL (0)
+#define NULL __null
#else
#define NULL ((void*)0)
#endif
This has been the case since 1996, and since 2012 Clang includes a
work-around the very bug I'm trying to fix in this patch.
> Your code should not
> assume `NULL` is an expression whose size is a pointer.
This is code found in the wild that obeys the convention followed by
every other distribution, and there's no reason mingw-w64 should diverge.
Even /if/ this weren't the case, mingw-w64 /already/ uses the conventional
#define NULL __null
in /some/ headers, but not others. Even /if/ this is legal,
having inconsistent NULL values is undesirable
and fixing it to be consistent is also a good goal.
Please reconsider.
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