restore type of NULL to void * except when used in C++ programs

unfortunately this eliminates the ability of the compiler to diagnose
some dangerous/incorrect usage, but POSIX requires (as an extension to
the C language, i.e. CX shaded) that NULL have type void *. plain C
allows it to be defined as any null pointer constant.

the definition 0L is preserved for C++ rather than reverting to plain
0 to avoid dangerous behavior in non-conforming programs which use
NULL as a variadic sentinel. (it's impossible to use (void *)0 for C++
since C++ lacks the proper implicit pointer conversions, and other
popular alternatives like the GCC __null extension seem non-conforming
to the standard's requirements.)

8 files changed, 33 insertions, 0 deletions

diff --git a/include/locale.h b/include/locale.h
index 7e80fd93..ce384381 100644
--- a/include/locale.h
+++ b/include/locale.h
@@ -7,7 +7,11 @@ extern "C" {
 
 #include <features.h>
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
 
 #define LC_CTYPE    0
 #define LC_NUMERIC  1
diff --git a/include/stddef.h b/include/stddef.h
index 9d522486..0a329190 100644
--- a/include/stddef.h
+++ b/include/stddef.h
@@ -1,7 +1,11 @@
 #ifndef _STDDEF_H
 #define _STDDEF_H
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
 
 #define __NEED_ptrdiff_t
 #define __NEED_size_t
diff --git a/include/stdio.h b/include/stdio.h
index cd60bb55..884d2e6a 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -21,7 +21,11 @@ extern "C" {
 
 #include <bits/alltypes.h>
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
 
 #undef EOF
 #define EOF (-1)
diff --git a/include/stdlib.h b/include/stdlib.h
index 2bd5f102..1e67b896 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -7,7 +7,11 @@ extern "C" {
 
 #include <features.h>
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
 
 #define __NEED_size_t
 #define __NEED_wchar_t
diff --git a/include/string.h b/include/string.h
index d4412333..ff9badb9 100644
--- a/include/string.h
+++ b/include/string.h
@@ -7,7 +7,11 @@ extern "C" {
 
 #include <features.h>
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
 
 #define __NEED_size_t
 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
diff --git a/include/time.h b/include/time.h
index 6e499ffe..70574093 100644
--- a/include/time.h
+++ b/include/time.h
@@ -7,7 +7,12 @@ extern "C" {
 
 #include <features.h>
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
+
 
 #define __NEED_size_t
 #define __NEED_time_t
diff --git a/include/unistd.h b/include/unistd.h
index a00a9c4f..9f2fac96 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -15,7 +15,11 @@ extern "C" {
 #define SEEK_CUR 1
 #define SEEK_END 2
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
 
 #define __NEED_size_t
 #define __NEED_ssize_t
diff --git a/include/wchar.h b/include/wchar.h
index fd5aac5f..9fd967cc 100644
--- a/include/wchar.h
+++ b/include/wchar.h
@@ -33,7 +33,11 @@ extern "C" {
 #define WCHAR_MIN (-1-0x7fffffff+L'\0')
 #endif
 
+#ifdef __cplusplus
 #define NULL 0L
+#else
+#define NULL ((void*)0)
+#endif
 
 #undef WEOF
 #define WEOF 0xffffffffU