Re: strnlen.h

[Simon Josefsson]

Paul Eggert <address@hidden> writes:

> "Mark D. Baushke" <address@hidden> writes:
>
>> If you must check for it being defined, wouldn't this form
>>
>> #if !defined HAVE_DECL_STRNLEN || !HAVE_DECL_STRNLEN
>
> In the old days we were worried about people using gnulib .c files
> without using the corresponding .m4 code.  In such a case,
> HAVE_DECL_STRNLEN wouldn't be defined, but the code still shouldn't
> declare strnlen.
>
> These days the gnulib packaging process pretty much makes these
> concerns obsolete.  So it's OK to use "#if !HAVE_DECL_STRNLEN"
> nowadays, I think.

The autoconf manual still suggests to use the former.  Perhaps that
wording can be relaxed further...

     Unlike the other `AC_CHECK_*S' macros, when a SYMBOL is not
     declared, `HAVE_DECL_SYMBOL' is defined to `0' instead of leaving
     `HAVE_DECL_SYMBOL' undeclared.  When you are _sure_ that the check
     was performed, use `HAVE_DECL_SYMBOL' just like any other result
     of Autoconf:

          #if !HAVE_DECL_SYMBOL
          extern char *symbol;
          #endif

     If the test may have not been performed, however, because it is
     safer _not_ to declare a symbol than to use a declaration that
     conflicts with the system's one, you should use:

          #if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC
          void *malloc (size_t *s);
          #endif

     You fall into the second category only in extreme situations:
     either your files may be used without being configured, or they
     are used during the configuration.  In most cases the traditional
     approach is enough.