[R] returning strings to R from C functions
maechler at stat.math.ethz.ch
Thu Jun 3 09:11:36 CEST 2004
>>>>> "Fernando" == Fernando Pineda <fernando.pineda at jhu.edu>
>>>>> on Wed, 2 Jun 2004 23:22:22 -0400 writes:
Fernando> I'm using .C() and .External() and have no
Fernando> problems sending integers, reals or strings from R
Fernando> to C. Nor do I have problems sending integers or
Fernando> reals back from C to R. But I'm pulling my hair
Fernando> out trying to set a string value in a C function
Fernando> and then sending it back from C to to R. I've
Fernando> searched the usual sources and tried various
Fernando> casts, macros and allocation schemes, but I'm
Fernando> failing miserably. Could someone please put me out
Fernando> of my misery and point me to a working example?
You did read the section entitled
"Interface functions `.C' and `.Fortran'"
in the "Writing R Extensions" manual ?
>> The following table gives the mapping between the modes of R vectors
>> and the types of arguments to a C function or FORTRAN subroutine.
>> R storage mode C type FORTRAN type
>> `logical' `int *' `INTEGER'
>> `integer' `int *' `INTEGER'
>> `double' `double *' `DOUBLE PRECISION'
>> `complex' `Rcomplex *' `DOUBLE COMPLEX'
>> `character' `char **' `CHARACTER*255'
One working example is the R function formatC()
with the C code in <Rsource>/src/appl/strsignif.c
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