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Re: [PATCH] Use mode_t in open and friends

On 05/03/2014 10:28 AM, OndÅej BÃlka wrote:
> On Thu, Apr 24, 2014 at 02:30:21PM +0200, Andreas Schwab wrote:
>> Rasmus Villemoes <> writes:
>>> The sole varargs argument to open and friends has type mode_t, not int.
>> Varargs use the promoted type, but mode_t traditionally has been
>> unsigned short.
> So which solution do you prefer? Adding a custom type for that as
> suggested in sibling threads? What about just adding a cast like
> mode = (mode_t) va_arg (arg, int);

Might be overkill for this instance alone, but another option
would be letting the compiler do the work.  It avoids having
to care whether mode_t might be wider than int, or unsigned.

Can be done with C11's _Generic, or GCC's

Here's how it might look with the latter:

mode = __unpromoted_va_arg (arg, mode_t);

#define __maybe_va_arg(list, type, unpromoted, promoted, else_expr)	  \
  __builtin_choose_expr (__builtin_types_compatible_p (type, unpromoted), \
			 va_arg (list, promoted),			  \

/* Like va_arg, but accepts unpromoted types.  */
#define __promoted_va_arg(list, type)					\
  (type) __maybe_va_arg (list, type, float, double,			\
	 __maybe_va_arg (list, type, char, int,				\
	 __maybe_va_arg (list, type, short int, int,			\
	 __maybe_va_arg (list, type, unsigned char, unsigned int,	\
	 __maybe_va_arg (list, type, unsigned short int, unsigned int,	\
	 va_arg (list, type))))))

Pedro Alves

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