On Thu, 2011-04-28 at 13:40 +0200, Csaba Halász wrote:
[]
> NULL has never been officially defined in any C++ header that I know.
> So code that relies on that is broken.
[]
Hi Csaba,
It is interesting you say that... do you have a reference?
Always interested to learn, know more ;=))
But the 2 simple examples given previously :-
// temp1.cxx
#include <stdio.h>
int main(int argc, char *argv[])
{
char * cp = NULL;
#ifdef NULL
printf("NULL is defined ok\n");
#else
printf("NULL is NOT defined\n");
#endif
}
and
// temp2.cxx
int main(int argc, char *argv[])
{
char * cp = NULL;
#ifdef NULL
printf("NULL is defined ok\n");
#else
// printf("NULL is NOT defined\n");
#endif
}
Then running g++ on each...
~/test$ g++ temp1.cxx
~/test$ ./a.out
NULL is defined ok
No problem, then
~/test$ g++ temp2.cxx
temp2.cxx: In function ‘int main(int, char**)’:
temp2.cxx:4: error: ‘NULL’ was not declared in this scope
What am I missing here? ;=))
Does that not indicate NULL is defined in <stdio.h>, or
in another header included by it, or do you not consider
this a C++ header? Or something...
In libio.h, included by stdio.h, I can see a
block :-
#ifndef NULL
# if defined __GNUG__ && \
(__GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8))
# define NULL (__null)
# else
# if !defined(__cplusplus)
# define NULL ((void*)0)
# else
# define NULL (0)
# endif
# endif
#endif
Just to understand...
Regards,
Geoff.
PS: ~/test$ g++ --version
g++ (Ubuntu 4.4.3-4ubuntu5) 4.4.3
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