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10.1258 va_arg

POSIX specification:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/va_arg.html

Gnulib module: —

Portability problems fixed by Gnulib:

Portability problems not fixed by Gnulib:

• The second argument of va_arg must be a type that is invariant under the “default argument promotions” (ISO C 99 6.5.2.2 paragraph 6). This means that the following are not valid here:

  ‘float’

  Use ‘double’ instead.

  ‘bool’

  Use ‘int’ instead.

  Integer types smaller than ‘int’.

  Use ‘int’ or ‘unsigned int’ instead.

  This is a portability problem because you don’t know the width of some abstract types like uid_t, gid_t, mode_t. So, instead of

  mode = va_arg (ap, mode_t);
  

  you have to write

  mode = (sizeof (mode_t) < sizeof (int)
          ? va_arg (ap, int)
          : va_arg (ap, mode_t));