problem building an R package under Windows XP with calls to

I this more complex package, I use several calls to "printf" in the C
program of that package. I also use "cat" calls in the R function of the
package. It turns out that all calls to "cat" work without problem
whereas calls to "printf" always fail (i.e. nothing is displayed in R).
What is also interesting is that the calls to "printf" are however all
displayed after I quit R. So it looks like it is R that does not allow
my C program to display text on the standard output. This is very
surprising because the simple package "test" I described above does work
just fine even though it also uses "printf" calls.