MB_LEN_MAX - maximum multibyte length of a character across all locales

       The  MB_LEN_MAX  macro is the maximum number of bytes needed to represent a single wide character, in any
       of the supported locales.

       C99, POSIX.1-2001.

       Standard C library (libc)

       MB_LEN_MAX - maximum multibyte length of a character across all locales

       The entities MB_LEN_MAX and sizeof(wchar_t) are totally unrelated.  In glibc, MB_LEN_MAX is typically  16
       (6 in glibc versions earlier than 2.2), while sizeof(wchar_t) is 4.

       A constant integer greater than zero.

MB_CUR_MAX(3)

Linux man-pages 6.9.1                              2024-05-02                                      MB_LEN_MAX(3)

       C11, POSIX.1-2008.

#include<limits.h>