[Rd] a R_PV problem

[pseudo]

Dear all,

When using gdb to debug my C code, I use R_PV to show the content of
SEXP variables:

  SEXP sexp; // it is a data.frame
  SEXP colNames = getAttrib(sexp, R_NameSymbol);

A strange thing is that after halting the program:

  (gdb) p R_PV(colNames)

does not show the content of colNames. I am positive my code is right
because if I insert "PrintValue(colNames);" in the c code, it will
print the right value. My debug result shows that the variable
"colNames" failed the "isObject" call. I am not sure whether this is a
new feature or bug. Anyone can help?

Thanks,

Gang Liang