R devel - May 2016 - Suggestion: mkString(NULL) should be NA

I would like to propose that Rf_mkString(NULL) and Rf_mkChar(NULL)
return NA rather than segfault.

Case: the mkString() and mkChar() functions are convenient to wrap
strings returned by e.g. external C libraries into an R vector.
However sometimes a library returns NULL instead of a string when the
result is unavailable. In some C libraries this can happen
unexpectedly or is even undocumented.

A good R package author always checks results for a null pointer, and
deals with it accordingly. But sometimes we make assumptions. There
was an example in the 'curl' package where a documented version string
was suddenly NULL if libcurl was built with some unusual
configuration. These problems are hard to catch and I don't see any
benefit of segfaulting for such edge cases.

Some packages use a macro like this to protect against such problems:

  #define make_string(x) x ? Rf_mkString(x) : ScalarString(NA_STRING)

But I think it would make sense if this was the default behavior in
Rf_mkString and Rf_mkChar.

On Thu, May 12, 2016 at 1:20 PM, Jeroen Ooms <jeroen.ooms at
stat.ucla.edu> wrote:
> I would like to propose that Rf_mkString(NULL) and Rf_mkChar(NULL)
> return NA rather than segfault.
An example implementation: https://git.io/vroxm

With this patch, mkChar(NULL), mkCharCE(NULL, ce) would return
NA_STRING rather than segfault at strlen(NULL). This automatically
fixes mkString(NULL) as well which wraps mkChar (See Rinlinedfuns.h).

Shouldn't Rf_mkString(NULL) return (the c-level equivalent of) character()
rather than the NA_character_? An empty string and NULL aren't the same. It
seems reasonable for Rf_mkChar to give NA_character_ though.

~G

On Tue, May 24, 2016 at 8:42 AM, Jeroen Ooms <jeroen.ooms at
stat.ucla.edu>
wrote:
> On Thu, May 12, 2016 at 1:20 PM, Jeroen Ooms <jeroen.ooms at
stat.ucla.edu>
> wrote:
> > I would like to propose that Rf_mkString(NULL) and Rf_mkChar(NULL)
> > return NA rather than segfault.
>
> An example implementation: https://git.io/vroxm
>
> With this patch, mkChar(NULL), mkCharCE(NULL, ce) would return
> NA_STRING rather than segfault at strlen(NULL). This automatically
> fixes mkString(NULL) as well which wraps mkChar (See Rinlinedfuns.h).
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>


-- 
Gabriel Becker, PhD
Associate Scientist (Bioinformatics)
Genentech Research

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Why should Rf_mkString(NULL) produce NA_STRING instead of ""
(R_BlankString)?  I prefer that passing in a nil pointer would cause
an error instead, as the nil may arise by accident, perhaps a pointer
to freed memory, and I would like to be notified that my code is bad instead
of getting a random NA_STRING.


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, May 24, 2016 at 8:42 AM, Jeroen Ooms <jeroen.ooms at
stat.ucla.edu>
wrote:
> On Thu, May 12, 2016 at 1:20 PM, Jeroen Ooms <jeroen.ooms at
stat.ucla.edu>
> wrote:
> > I would like to propose that Rf_mkString(NULL) and Rf_mkChar(NULL)
> > return NA rather than segfault.
>
> An example implementation: https://git.io/vroxm
>
> With this patch, mkChar(NULL), mkCharCE(NULL, ce) would return
> NA_STRING rather than segfault at strlen(NULL). This automatically
> fixes mkString(NULL) as well which wraps mkChar (See Rinlinedfuns.h).
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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