mbsinit - test for initial shift state


Standard C library (libc, -lc)


#include <wchar.h>
int mbsinit(const mbstate_t *ps);


Character conversion between the multibyte representation and the wide character representation uses conversion state, of type mbstate_t. Conversion of a string uses a finite-state machine; when it is interrupted after the complete conversion of a number of characters, it may need to save a state for processing the remaining characters. Such a conversion state is needed for the sake of encodings such as ISO/IECĀ 2022 and UTF-7.

The initial state is the state at the beginning of conversion of a string. There are two kinds of state: the one used by multibyte to wide character conversion functions, such as mbsrtowcs(3), and the one used by wide character to multibyte conversion functions, such as wcsrtombs(3), but they both fit in a mbstate_t, and they both have the same representation for an initial state.

For 8-bit encodings, all states are equivalent to the initial state. For multibyte encodings like UTF-8, EUC-*, BIG5, or SJIS, the wide character to multibyte conversion functions never produce non-initial states, but the multibyte to wide-character conversion functions like mbrtowc(3) do produce non-initial states when interrupted in the middle of a character.

One possible way to create an mbstate_t in initial state is to set it to zero:

mbstate_t state;
memset(&state, 0, sizeof(state));

On Linux, the following works as well, but might generate compiler warnings:

mbstate_t state = { 0 };

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).

Interface Attribute Value


Thread safety MT-Safe


C11, POSIX.1-2008.


POSIX.1-2001, C99.


The behavior of mbsinit() depends on the LC_CTYPE category of the current locale.


mbrlen(3), mbrtowc(3), mbsrtowcs(3), wcrtomb(3), wcsrtombs(3)