R devel - Aug 2005 - wchar and wstring.

Hello all, I am writing an R interface to some C++ files which make use
of std::wstring classes for internationalization. Previously (when I
wanted to make R strings from C++ std::strings), I would do something
like this to construct a string in R from the results of the parse.

SET_VECTOR_ELT(vals, i++, mkString(header.GetHeader().c_str()));


However, now the call header.GetHeader().c_str() returns a pointer to an
array of wchar_t's. I was going to use
wcstombs() to convert the wchar_t* to char*, but I wanted to see if
there was a similar function in R for the mkString function which I had
initially used which deals with wchar_ts as opposed to chars. Also,
since I have no experience with the wctombs() function I wanted to ask
if anyone knew if this will handle the internationilzation issues from
within R.


As always thank you for the help. jim

On Fri, 26 Aug 2005, James Bullard wrote:
> Hello all, I am writing an R interface to some C++ files which make use
> of std::wstring classes for internationalization. Previously (when I
> wanted to make R strings from C++ std::strings), I would do something
> like this to construct a string in R from the results of the parse.
>
> SET_VECTOR_ELT(vals, i++, mkString(header.GetHeader().c_str()));
That creates a list of one-element character vectors.  It would be more
usual to do

   SET_STRING_ELT(vals, i++, mkChar(header.GetHeader().c_str()));
> However, now the call header.GetHeader().c_str() returns a pointer to an 
> array of wchar_t's. I was going to use wcstombs() to convert the 
> wchar_t* to char*, but I wanted to see if there was a similar function 
> in R for the mkString function which I had initially used which deals 
> with wchar_ts as opposed to chars.
No (nor an analogue of mkChar).  R uses MBCS and not wchar_t internally 
(and Unix-alike systems do externally).  There is no wchar_t internal R 
type (a much-debated design decision at the time).
> Also, since I have no experience with the wctombs() function I wanted to 
> ask if anyone knew if this will handle the internationilzation issues 
> from within R.
Did you mean wcstombs or wctomb (if the latter, wcrtomb is preferred)?
There are tens of examples in the R sources for you to consult.

Note that not all R platforms support wchar_t, hence this code is 
surrounded by #ifdef SUPPORT_MBCS macros (exported in Rconfig.h for 
package writers).

-- 
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