8017 Comply with POSIX.1-2008 and C++11 for the definition of NULL

@@ -14,16 +14,39 @@
  */
 
 #ifndef _SYS_NULL_H
 #define _SYS_NULL_H
 
+#include <sys/feature_tests.h>
+
 #ifndef NULL
 
+/*
+ * POSIX.1-2008 requires that the NULL macro be cast to type void *.
+ * Historically, this has not been done, so we only enable this in a
+ * POSIX.1-2008 compilation environment.
+ */
+
+#if defined(_XPG7) && !defined(__cplusplus)
+#define NULL    ((void *)0)
+#else
+
+/*
+ * ISO C++ requires that the NULL macro be defined as a constant integral
+ * type evaluating to zero until C++11, and an integer or pointer literal
+ * with value zero from C++11 onwards.
+ */
+
+#if defined(__cplusplus) && __cplusplus >= 201103L
+#define NULL    nullptr
+#else
 #if defined(_LP64)
 #define NULL    0L
 #else
 #define NULL    0
-#endif
+#endif  /* _LP64 */
+#endif  /* C++11 */
+#endif  /* _XPG7 */
 
 #endif  /* NULL */
 
 #endif  /* _SYS_NULL_H */