.Call interface: Use R SEXP as C mutable *char

Dear R Developers,


DISCLAIMER: I am new to package development in R and new to this list.

I am trying to do something along the lines of:

SEXP test_fun (SEXP filename) {

const char *inputfile = translateChar(STRING_ELT(filename, 0));

int abc = some_function(inputfile);

...

}

The code compiles fine, but I get a warning:
"passing argument of 'some_function' discards qualifiers from pointer 
target type"

I read up on my issue and found this posting:
https://stat.ethz.ch/pipermail/r-devel/2011-June/061221.html

I gather that the 'some_function' (which is a function from another 
library) takes just '*char' as argument type so the 'const' qualifier is 
discarded.

Of course I want my package to compile without warnings. All my other 
attempts led to similar 'discard' warnings (mainly initializations of 
helper variables).

What is the recommended approach here?

Best Regards,
Michael Bach