Is there a way to return POSIXct object to R from C?

Question

I want to create a vector of datetime object in C/C++ and then return them to R. In the documentation of POSIXct class it is written that it keeps seconds since 1970-01-01 as a vector of numeric values, so I guess there should be a way to do the conversion from double to POSIXct in C.

I have this C code and want to return POSIXct dates instead of REAL numbers.

SEXP func()
{
    SEXP dates;
    PROTECT(dates = allocVector(REALSXP, 2));
    REAL(dates)[0] = 1402329599.12456;
    REAL(dates)[1] = 1402329600.85404;
    UNPROTECT(1);
    return dates;
}

Answer 1

Easy as setting the class .

#include <R.h>
#include <Rdefines.h>

SEXP func()
{
    SEXP dates, class;
    PROTECT(dates = allocVector(REALSXP, 2));
    REAL(dates)[0] = 1402329599.12456;
    REAL(dates)[1] = 1402329600.85404;

    class = PROTECT(allocVector(STRSXP, 2));
    SET_STRING_ELT(class, 0, mkChar("POSIXct"));
    SET_STRING_ELT(class, 1, mkChar("POSIXt"));
    classgets(dates, class);

    UNPROTECT(2);
    return dates;
}

You might also want to set the tzone attribute.

#include <R.h>
#include <Rdefines.h>

SEXP func()
{
    SEXP dates, class, tz_attr;
    PROTECT(dates = allocVector(REALSXP, 2));
    REAL(dates)[0] = 1402329599.12456;
    REAL(dates)[1] = 1402329600.85404;

    class = PROTECT(allocVector(STRSXP, 2));
    SET_STRING_ELT(class, 0, mkChar("POSIXct"));
    SET_STRING_ELT(class, 1, mkChar("POSIXt"));
    classgets(dates, class);

    tz_attr = PROTECT(allocVector(STRSXP, 1));
    SET_STRING_ELT(tz_attr, 0, mkChar("GMT"));
    setAttrib(dates, install("tzone"), tz_attr);

    UNPROTECT(3);
    return dates;
}

Answer 2

你可以从R做强制：

r_func <- function( tz=NULL) .POSIXct(.Call("func"), tz)