[Rd] Question about copying arguments in C.

Simon Knapp simon.knapp at anu.edu.au
Sat Sep 15 05:10:05 CEST 2012

Hi List,

I'd imagine this is a question that has been answered before, but I
can't seem to track it down, sorry for the duplication if it has.

I am writing an interface for a C library and want to return an S4
class from the 'constructing' method. One of the slots of the argument
to be returned will be filled with one of the arguments passed to the
function. My question is about whether I can directly pass arguments
to the function directly to slots of the returned object (or to a
return value more generally for that matter), or whether I have to
copy them. If it is the latter, then how may I do this. The question
is phrased in the following (simplified) code.

int constructThingy(int thingysInteger);

SEXP constructThingy(SEXP thingysInteger) {
    SEXP ans, TClass, ti;
    if(!isInteger(thingysInteger)) error("thingysIntegermust be an integer.");
    if(constructThingy(INTEGER(thingysInteger)[0])) error("error in
getting a thingy");
    TClass = MAKE_CLASS("thingy");
    PROTECT(ans = NEW_OBJECT(TClass));

    // *****QUESTION STARTS HERE*****
    // CAN I SAY:
    SET_SLOT(ans, Rf_install("myInteger"), thingysInteger);

    // IF NOT, CAN I SAY
    SET_SLOT(ans, Rf_install("myInteger"), AS_INTEGER(thingysInteger));

    PROTECT(ti = allocVector(INTSXP, 1)); INTEGER(pns)[0] =
    SET_SLOT(ans, Rf_install("myInteger"), ti);
    // *****END OF QUESTION*****

    UNPROTECT(1); // or UNPROTECT(2) in latter case.
    return ans;

I think this is the same as asking whether the following is OK:

SEXP func(SEXP arg) {
    return arg;

Thanks in advance,

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