[Rd] Memory Protection & calling C-fun from C
Torsten Hothorn
Torsten.Hothorn at rzmail.uni-erlangen.de
Fri Apr 2 08:39:59 CEST 2004
Good morning!
The descriptions of memory protection all assume that one
is calling a C-function directly from R. I'm not sure if my
understanding of calling a C-function from another C-function
is correct:
Suppose there are two functions
SEXP bar(SEXP y) {
SEXP b;
PROTECT(b = allocVector(...));
... computations on b
UNPROTECT(1);
return b
}
and
SEXP foo(SEXP x) {
SEXP a;
PROTECT(a = bar(x)); /* use bar to do lowlevel computations */
... futher computations on a
UNPROTECT(1);
return a;
}
Of course,
R> .Call("bar", x)
is safe but is
R> .Call("foo", x)
too? May it happen that the object `b' points to is destroyed before it is
protected by `PROTECT(a = bar(x))'?
I searched for examples of that in R and some packages but did only find
some where `bar' is defined by
double* bar(double *y)
and the problems do not occur. Anyway, I want to be able to call both
`foo' and `bar' directly from R and C-level (say for the sake of writing
tests in R for the lowlevel functions).
Any clarification is very welcome && Thanks in advance,
Torsten
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