test for initial shift state
Standard C library (libc, -lc)
The function mbsinit() tests whether *ps corresponds to an initial state.
mbsinit() returns nonzero if *ps is an initial state, or if ps is NULL. Otherwise, it returns 0.
For an explanation of the terms used in this section, see attributes(7).
C11, POSIX.1-2008.
POSIX.1-2001, C99.
The behavior of mbsinit() depends on the LC_CTYPE category of the current locale.