The file ctype.c contains 13 different functions (isalnum, isalpha, iscntrl, isdigit, islower, isgraph, isprint, ispunct, isspace, isupper, isxdigit, tolower, and toupper). Trying to use other implementations of one or more of those functions, say toupper and tolower, will cause conflicts during linking if any of the other functions in ctype.c are used. One has to define __NO_INLINE__ or use some other way to prevent inlining of the ctype functions for the conflict to occur.
You are not supposed to replace functions. If you do you're on your own and then don't dare to come here ad complain.
(In reply to comment #1) > You are not supposed to replace functions. If you do you're on your own and then > don't dare to come here ad complain. Ok, I stand corrected and I'm sorry for wasting your time, but... There are reasons why some people would like to use other implementations of some function in the C library, typically to reduce the code size. Is there any point in making that unnecessarily hard to do that?