Well, no. If you make a #define it will affect code in the #include. This is why you sees puts defined as extern int puts(__const char *__s); The reason

Well, no. If you make a #define it will affect code in the #include. This is why you sees puts defined as extern int puts(__const char *__s); The reason for the double underscore is so the definitions won't be affected if 's' is a macro.