# mbrtowc

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           mbrtowc — convert a character to a wide-character code
           (restartable)
    


## SYNOPSIS



           #include <wchar.h>
    
           size_t mbrtowc(wchar_t *restrict _pwc_ , const char *restrict _s_ ,
               size_t _n_ , mbstate_t *restrict _ps_);
    


## DESCRIPTION



           The functionality described on this reference page is aligned with
           the ISO C standard. Any conflict between the requirements
           described here and the ISO C standard is unintentional. This
           volume of POSIX.1‐2017 defers to the ISO C standard.
    
           If _s_ is a null pointer, the _mbrtowc_() function shall be equivalent
           to the call:
    
               mbrtowc(NULL, "", 1, ps)
    
           In this case, the values of the arguments _pwc_ and _n_ are ignored.
    
           If _s_ is not a null pointer, the _mbrtowc_() function shall inspect
           at most _n_ bytes beginning at the byte pointed to by _s_ to determine
           the number of bytes needed to complete the next character
           (including any shift sequences). If the function determines that
           the next character is completed, it shall determine the value of
           the corresponding wide character and then, if _pwc_ is not a null
           pointer, shall store that value in the object pointed to by _pwc_.
           If the corresponding wide character is the null wide character,
           the resulting state described shall be the initial conversion
           state.
    
           If _ps_ is a null pointer, the _mbrtowc_() function shall use its own
           internal **mbstate_t** object, which shall be initialized at program
           start-up to the initial conversion state. Otherwise, the **mbstate_t**
           object pointed to by _ps_ shall be used to completely describe the
           current conversion state of the associated character sequence. The
           implementation shall behave as if no function defined in this
           volume of POSIX.1‐2017 calls _mbrtowc_().
    
           The behavior of this function is affected by the _LC_CTYPE_ category
           of the current locale.
    
           The _mbrtowc_() function need not be thread-safe if called with a
           NULL _ps_ argument.
    
           The _mbrtowc_() function shall not change the setting of _errno_ if
           successful.
    


## RETURN VALUE



           The _mbrtowc_() function shall return the first of the following
           that applies:
    
           0           If the next _n_ or fewer bytes complete the character
                       that corresponds to the null wide character (which is
                       the value stored).
    
           between 1 and _n_ inclusive
                       If the next _n_ or fewer bytes complete a valid
                       character (which is the value stored); the value
                       returned shall be the number of bytes that complete
                       the character.
    
           (**size_t**)-2  If the next _n_ bytes contribute to an incomplete but
                       potentially valid character, and all _n_ bytes have been
                       processed (no value is stored). When _n_ has at least
                       the value of the {MB_CUR_MAX} macro, this case can
                       only occur if _s_ points at a sequence of redundant
                       shift sequences (for implementations with state-
                       dependent encodings).
    
           (**size_t**)-1  If an encoding error occurs, in which case the next _n_
                       or fewer bytes do not contribute to a complete and
                       valid character (no value is stored). In this case,
                       **[EILSEQ]** shall be stored in _errno_ and the conversion
                       state is undefined.
    


## ERRORS



           The _mbrtowc_() function shall fail if:
    
           **EILSEQ** An invalid character sequence is detected.  In the POSIX
                  locale an **[EILSEQ]** error cannot occur since all byte values
                  are valid characters.
    
           The _mbrtowc_() function may fail if:
    
           **EINVAL** _ps_ points to an object that contains an invalid conversion
                  state.
    
           _The following sections are informative._
    


## EXAMPLES



           None.
    


## APPLICATION USAGE



           None.
    


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


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