Re: [PATCH,RFC] Change __convert_from_v to use snprintf and use it

[Paolo Carlini <pcarlini at unitus dot it>]

Benjamin Kosnik wrote:

> > Thanks once more. I admit to be very ignorant about those matters. I'm indeed /very/ happy
> > to know that snprintf can be used when available (in the form standardized as part of C99,
> > indeed!)
>
> Yep.

Indeed an AC_TRY_COMPILE for snprintf is already part of the set of tests in acinclude.m4 for
_GLIBCPP_USE_C99.

Good.

However, I'm a bit nervous about this: what if _GLIBCPP_USE_C99 becomes true but in fact
snprintf is /not/ C99-conforming? In fact, I'm aware of pre-C99 snprintf which returned -1 in
case of too small buffer. This would be really bad.

Is it safe to assume that if _GLIBCPP_USE_C99 is defined then the libc is C99 conforming and
therefore snprintf will behave correctly at run time? (vs the -1 problem, I mean)

> Great! I look forward to seeing this.

One more bit of advice :-) ...

In my tree __convert_from_v is now tentatively as below. Notice the dummy if(__size); to
silence warnings about an unused parameter in case !C99. What do you suggest about this? Is
there a much cleaner way to solve the trouble with __size when !C99 ???

Thanks,
Paolo.

//////////////

  template<typename _Tv>
    int
    __convert_from_v(char* __out, const int __size, const char* __fmt, _Tv __v,
       const __c_locale&, int __prec = -1)
    {
      int __ret;
      const char* __old = setlocale(LC_ALL, "C");
      if (__prec >= 0)
#if defined(_GLIBCPP_USE_C99)
        __ret = snprintf(__out, __size, __fmt, __prec, __v);
#else
        __ret = sprintf(__out, __fmt, __prec, __v);
#endif
      else
#if defined(_GLIBCPP_USE_C99)
        __ret = snprintf(__out, __size, __fmt, __v);
#else
        __ret = sprintf(__out, __fmt, __v);
#endif
      if (__size); // Only to silence warnings.
      setlocale(LC_ALL, __old);
      return __ret;
    }