Question about ULLONG_MAX

Question about ULLONG_MAX

[Holger Kiehl]

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.

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?

Thanks,
Holger

Re: Question about ULLONG_MAX

[Stephen Kratzer]

From limits.h,

#  ifdef __USE_ISOC99

/* Minimum and maximum values a `signed long long int' can hold.  */
#   define LLONG_MAX    9223372036854775807LL
#   define LLONG_MIN    (-LLONG_MAX - 1LL)

/* Maximum value an `unsigned long long int' can hold.  (Minimum is 0.)  */
#   define ULLONG_MAX   18446744073709551615ULL

#  endif /* ISO C99 */


/* The <limits.h> files in some gcc versions don't define LLONG_MIN,
   LLONG_MAX, and ULLONG_MAX.  Instead only the values gcc defined for
   ages are available.  */
#if defined __USE_ISOC99 && defined __GNUC__
# ifndef LLONG_MIN
#  define LLONG_MIN     (-LLONG_MAX-1)
# endif
# ifndef LLONG_MAX
#  define LLONG_MAX     __LONG_LONG_MAX__
# endif
# ifndef ULLONG_MAX
#  define ULLONG_MAX    (LLONG_MAX * 2ULL + 1)
# endif
#endif

On Monday 02 July 2007 04:55:00 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.
>
> 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?
>
> Thanks,
> Holger
>
> -
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Re: Question about ULLONG_MAX

[Glynn Clements]

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@gclements.plus.com>

Re: Question about ULLONG_MAX

[Holger Kiehl]

On Mon, 2 Jul 2007, Glynn Clements wrote:

>
> Holger Kiehl wrote:
>
>> 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.
>
You are right. Enabling C99 support explicitly is the better solution.

Thanks,
Holger