You may be able to use vprintf and family to do this more reliably and without needing metaprogramming at all, but unfortunately the definition of va_list is equally ill defined by the C standards. At least this avoids call-time ABI problems, however.
On Mon, Apr 21, 2014 at 10:17 AM, Jameson Nash <[email protected]> wrote: > On anything but x86-32 or older processors, the output is undefined. > The compiler authors when ANSI C was introduced decided to sacrifice > performance in order to make the three ways of declaring a C function > (K&R-style without arguments, with arguments, and with varargs) to > generate the same code for the x86-legacy processors of that time. > > However, newer ABI's, such as the x64 platform standard, define these > function as using different rules for where to place the arguments, > depending on the value in another register that is left uninitialized > for non-variadic calls. > > On Win64, varargs are never placed in registers. On ARM, varargs are > never optimized in their register allocation > > On Mon, Apr 21, 2014 at 1:30 AM, Dominique Orban > <[email protected]> wrote: > > I posted some timings here but I think they went unnoticed because > they're > > buried in a conversation: > > https://groups.google.com/d/msg/julia-users/7Sn5yys0UJE/Fy8TyTNNQEQJ > > > > Jameson, could you be more specific? In what kind of situation would > printf > > give incorrect output? > > > > > > On Sunday, April 20, 2014 8:06:52 PM UTC-7, Jameson wrote: > >> > >> just as a vague warning, va_arg lists are similar to, but subtly > >> different from their fully specified counterparts. what this means is > >> that calling printf from julia will work most of the time, but will > >> also probably fail (by which I mean produce slightly incorrect output) > >> at random and at the worst possible time given the same inputs > >> > >> On Sun, Apr 20, 2014 at 10:22 PM, Kevin Squire <[email protected]> > >> wrote: > >> > Looks interesting. I'm not at a computer right now, so can't test. Can > >> > you > >> > give an example run? How are the timings? > >> > > >> > Kevin > >> > > >> > > >> > On Sunday, April 20, 2014, Dominique Orban <[email protected]> > >> > wrote: > >> >> > >> >> Here's how I wrapped printf, allowing for varargs: > >> >> https://gist.github.com/dpo/11000433 > >> >> I'd be interested in any comments. I expect it's possible to wrap > scanf > >> >> similarly?! > >> >> > >> >> On Friday, February 21, 2014 5:05:32 PM UTC-8, Stefan Karpinski > wrote: > >> >>> > >> >>> You could maybe make vscanf and company work though. In general, > using > >> >>> the c library for this kind of thing will be awkward. > >> >>> > >> >>> > On Feb 21, 2014, at 7:12 PM, "Steven G. Johnson" > >> >>> > <[email protected]> > >> >>> > wrote: > >> >>> > > >> >>> > Varargs functions like scanf won't work with ccall, in general. >
