The strxfrm function transforms a null-terminated string pointed to by src according to the current locale collation if any, then copies the transformed string into dst. Not more than n characters are copied into dst, including the terminating null character added. If n is set to 0 (it helps to determine an actual size needed for transformation), dst is permitted to be a NULL pointer.
Comparing two strings using strcmp after strxfrm is equal to comparing two original strings with strcoll.
Upon successful completion, strxfrm returns the length of the transformed string not including the terminating null character. If this value is n or more, the contents of dst are indeterminate.
setlocale(3), strcmp(3), strcoll(3), wcsxfrm(3)