[Rd] add Rvsnprintf to API ??

Prof Brian Ripley ripley at stats.ox.ac.uk
Sat May 14 08:56:05 CEST 2005

On Fri, 13 May 2005, Charles Geyer wrote:

> Could Rvsnprintf (in src/main/errors.c) be added to the R API
> with prototype in include/R_ext/Print.h say?
> Here's my problem.  I'm trying to write some code that is not
> totally tied to R.  Hence I want R style error messaging to
> be isolated in a small module.  I do not want #include <R.h>
> and calls to error (Rf_error) in most of my code.
> Hence I want to write a module with something like
> ----- begin code snippet -----
> #include <stdarg.h>
> #include <stdio.h>
> #include <R.h>
> #define BUFSIZE 1024
> void die(const char *format, ...)
> {
>    char buf[BUFSIZE];
>    va_list arg;
>    va_start(arg, format);
>    vsnprintf(buf, BUFSIZE, format, arg);
>    va_end(arg);
>    buf[BUFSIZE - 1] = '\0';
>    error(buf);
> }
> ----- end code snippet -----
> But that's not portable because vsnprintf isn't.
> You've already made a big effort to work around nonportability of
> vsnprintf, but don't make it available in the API.  Why not?
> If I could change vsnprintf to Rvsnprintf above, then I wouldn't
> have to do some horrible autoconf song and dance that probably wouldn't
> be completely portable anyway.
> Or is there a better solution I haven't seen?

R guarantees to have *vsnprintf* available.  Putting things in the API is 
a one-way decision and ties our hands for ever.  Rvsnprintf is not even 
exported from errors.c: it is static and just a convenience wrapper.

About all a user package needs to do is


and in your code snippet

extern int vsnprintf (char *str, size_t count, const char *fmt, va_list arg);

However, AFAIK all known R platforms do have vsnprintf these days: the 
MinGW compiler used on Windows gained it within the last year.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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