I'm new to R development, so this may be a trivial question.
In C, How do you convert a SEXP value returned by an R function to a
primitive C type (int, double, char, array, etc.)? I've tried using
the INTEGER(x), VECTOR_ELT(x,i), and similar functions found in /src/
include/Rinternals.h, but doing so results in incorrect results or a
seg-fault.
For example, I modified /tests/Embedding/Rerror.c so that it tries to
print the value returned by the function defined in error.R:
val = Test_tryEval(e, &errorOccurred);
printf("Returned: {%d}\n", VECTOR_ELT(val, 0) );
Where error.R is contains:
foo <-
function(x=3, y=6)
{
z <- x * y
z
}
But the output is just "0", not the correct "18". Any ideas?
Thanks for your help!
On Tue, 11 Jul 2006, Michael Petrovich wrote:> I'm new to R development, so this may be a trivial question. > > In C, How do you convert a SEXP value returned by an R function to a > primitive C type (int, double, char, array, etc.)? I've tried using > the INTEGER(x), VECTOR_ELT(x,i), and similar functions found in /src/ > include/Rinternals.h, but doing so results in incorrect results or a > seg-fault.See `Writing R Extensions', the documentation for that file. You cannot just guess that an object has the appropriate SEXPTYPE: you have to check it (or coerce to it). In your example it is likely to be a REALSXP (it could be an INTSXP), so you need to cover all possible cases.> For example, I modified /tests/Embedding/Rerror.c so that it tries to > print the value returned by the function defined in error.R: > > val = Test_tryEval(e, &errorOccurred); > printf("Returned: {%d}\n", VECTOR_ELT(val, 0) ); > > Where error.R is contains: > > foo <- > function(x=3, y=6) > { > z <- x * y > z > } > > But the output is just "0", not the correct "18". Any ideas? > > Thanks for your help!-- 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
Michael Petrovich wrote:> I'm new to R development, so this may be a trivial question. > > In C, How do you convert a SEXP value returned by an R function to a > primitive C type (int, double, char, array, etc.)? I've tried using > the INTEGER(x), VECTOR_ELT(x,i), and similar functions found in /src/ > include/Rinternals.h, but doing so results in incorrect results or a > seg-fault. > > For example, I modified /tests/Embedding/Rerror.c so that it tries to > print the value returned by the function defined in error.R: > > val = Test_tryEval(e, &errorOccurred); > printf("Returned: {%d}\n", VECTOR_ELT(val, 0) );Prof Ripley had already pointed you to the "Writing R extensions" manual, which explains this stuff in more details, and also hinted that most probably it is REALSXP instead of yours guesses. So I am just going to give a somewhat concrete example - you want to be doing something like this instead: val = Test_tryEval(e, &errorOccurred); switch( TYPEOF(val) ) { case REALSXP: printf("Returned: {%f}\n", REAL(val)[0]); break; case INTSXP: printf("Returned: {%d}\n", INTEGER(val)[0]); break; case STRSXP: printf("Returned: {%s}\n", CHAR(STRING_ELT(val, 0))); break; default: printf("Don't know what to do about type %d\n", TYPEOF(val)); }> > Where error.R is contains: > > foo <- > function(x=3, y=6) > { > z <- x * y > z > } > > But the output is just "0", not the correct "18". Any ideas? > > Thanks for your help! > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel