-extern uschar *string_copy(uschar *);
-extern uschar *string_copyn(uschar *, int);
-extern uschar *string_sprintf(const char *, ...) PRINTF_FUNCTION(1,2);
+extern uschar *string_copy(const uschar *);
+extern uschar *string_copyn(const uschar *, int);
+extern uschar *string_sprintf(const char *, ...) ALMOST_PRINTF(1,2);