R help - Jul 2005 - Passing character strings from C code to R

Hi,

I have a C code which produces array of integers and potentially a string,
and I have problems passing the string out. Here is the relevant part of the
code:

 1   PROTECT(Ret = allocVector(INTSXP, n));
 2   ret     = (int*) INTEGER(Ret);  /* get pointer to R's Ret */
 3   for(i=0; i<n; i++) ret[i] = data[i];
 4   Free(data);
 5   i=1;
 6   if (comment) { // comment was found
 7     n = strlen(comment);
 8     if(n>0) {    // and it actually have some length
 9        Rprintf(" '%s' %i\n", comment, n); 
 10       PROTECT(Str = allocString(n+1)); 
 11       str = CHAR(STRING_ELT(Str, 0));
 12       strcpy(str, comment);
 13       Rprintf(" '%s' %i\n", str, n);
 14       setAttrib(Ret, install("comm"), Str);
 15       i=2;
 16     }
 17     Free(comment);
 18   }
 20   UNPROTECT(i);  

Print statement in line 9 gives right results, but program crashes before
print statement in line 13.
Any ideas to what am I doing wrong? 

Jarek
=====================================\====                 
 Jarek Tuszynski, PhD.                               o / \ 
 Science Applications International Corporation  <\__,|  
 (703) 676-4192                        ">  \
 Jaroslaw.W.Tuszynski at saic.com                   `    \

Reading the posting guide would have shown you that R-help was quite 
inappropriate, so I have moved this to R-devel.

allocString does not allocate a character vector, which is what you 
want to set as an attribute (not a 'string', whatever that is).  (It 
creates a CHARSXP, a type that should not be user-visible directly and for 
which STRING_ELT is inappropriate.)

You want something like (PROTECTS omitted):

Str = allocVector(STRSXP, 1);
SET_STRING_ELT(Str, 0, mkChar(comment));

There are many similar examples in the R sources for you to browse.  There 
is even a shortcut that manages the PROTECTS,

Str = mkString(comment);

(That allocString and mkString return different types indicate why I wrote 
`whatever that is': the term is too loose to be useful.)

So you could just have

if(comment && strlen(comment)
    setAttrib(Ret, install("com"), mkString(comment));
if(comment) Free(comment);


On Fri, 15 Jul 2005, Tuszynski, Jaroslaw W. wrote:
> Hi,
>
> I have a C code which produces array of integers and potentially a string,
> and I have problems passing the string out. Here is the relevant part of
the
> code:
>
> 1   PROTECT(Ret = allocVector(INTSXP, n));
> 2   ret     = (int*) INTEGER(Ret);  /* get pointer to R's Ret */
> 3   for(i=0; i<n; i++) ret[i] = data[i];
> 4   Free(data);
> 5   i=1;
> 6   if (comment) { // comment was found
> 7     n = strlen(comment);
> 8     if(n>0) {    // and it actually have some length
> 9        Rprintf(" '%s' %i\n", comment, n);
> 10       PROTECT(Str = allocString(n+1));
> 11       str = CHAR(STRING_ELT(Str, 0));
> 12       strcpy(str, comment);
> 13       Rprintf(" '%s' %i\n", str, n);
> 14       setAttrib(Ret, install("comm"), Str);
> 15       i=2;
> 16     }
> 17     Free(comment);
> 18   }
> 20   UNPROTECT(i);
>
> Print statement in line 9 gives right results, but program crashes before
> print statement in line 13.
> Any ideas to what am I doing wrong?
-- 
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

Tuszynski, Jaroslaw W. wrote:
>Hi,
>
>I have a C code which produces array of integers and potentially a string,
>and I have problems passing the string out. Here is the relevant part of the
>code:
>
> 1   PROTECT(Ret = allocVector(INTSXP, n));
> 2   ret     = (int*) INTEGER(Ret);  /* get pointer to R's Ret */
> 3   for(i=0; i<n; i++) ret[i] = data[i];
> 4   Free(data);
> 5   i=1;
> 6   if (comment) { // comment was found
> 7     n = strlen(comment);
> 8     if(n>0) {    // and it actually have some length
> 9        Rprintf(" '%s' %i\n", comment, n); 
> 10       PROTECT(Str = allocString(n+1)); 
> 11       str = CHAR(STRING_ELT(Str, 0));
> 12       strcpy(str, comment);
> 13       Rprintf(" '%s' %i\n", str, n);
> 14       setAttrib(Ret, install("comm"), Str);
> 15       i=2;
> 16     }
> 17     Free(comment);
> 18   }
> 20   UNPROTECT(i);  
>
>Print statement in line 9 gives right results, but program crashes before
>print statement in line 13.
>Any ideas to what am I doing wrong? 
>
>Jarek
>=====================================\====                 
> Jarek Tuszynski, PhD.                               o / \ 
> Science Applications International Corporation  <\__,|  
> (703) 676-4192                        ">  \
> Jaroslaw.W.Tuszynski at saic.com                   `    \
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>  
>
SEXP charToSexp(char * val) {
  USER_OBJECT_ ans;
  PROTECT(ans = NEW_CHARACTER(1));
  if(val)
      SET_STRING_ELT(ans, 0, COPY_TO_USER_STRING(val));
  UNPROTECT(1);

  return(ans);
}

If you want to install comment attribute on return value set it this way
setAttrib(ans, R_CommentSymbol, charToSexp("Some comment"));