Holger Kiehl wrote:
> Hello
>
> When compiling the following program on a Fedora 6 x86_64 system:
>
> #include <stdio.h>
> #include <limits.h>
>
> int
> main(void)
> {
> (void)printf("%llu\n", ULLONG_MAX);
>
> return 0;
> }
>
> Produces the following result:
>
> cc longlong.c
> longlong.c: In function 'main':
> longlong.c:7: error: 'ULLONG_MAX' undeclared (first use in this function)
> longlong.c:7: error: (Each undeclared identifier is reported only once
> longlong.c:7: error: for each function it appears in.)
>
> If I compile it with cc -std=c99 longlong.c it works.
>
> Why is it necessary to specify -std=c99? If I use for example strtoull()
> I do not need to set -std=c99.
The declaration of strtoull() is enabled by __USE_MISC:
#if defined __USE_ISOC99 || (defined __GLIBC_HAVE_LONG_LONG && defined __USE_MISC)
If you use "-ansi -Wall", you'll get a warning due to the implicit
declaration of strtoull().
Bear in mind that a missing declaration only results in a warning,
while a missing macro is an error (as the symbol won't exist in any
library).
> Compiling the above on AIX compiles and runs without problems. Also
> on an older Solaris 8 system using gcc (3.3.2) it compiles and runs
> straight out of the box.
>
> If I want to use ULLONG_MAX how can I do this in a portable way so it
> compiles on different systems?
You need to explicitly enable C99 support; "long long" isn't in C89,
so you shouldn't assume that it will be available when using the
default compilation settings.
--
Glynn Clements <glynn@xxxxxxxxxxxxxxxxxx>
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