# mbsrtowcs

## 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



           mbsnrtowcs, mbsrtowcs — convert a character string to a wide-
           character string (restartable)
    


## SYNOPSIS



           #include <wchar.h>
    
           size_t mbsnrtowcs(wchar_t *restrict _dst_ , const char **restrict _src_ ,
               size_t _nmc_ , size_t _len_ , mbstate_t *restrict _ps_);
           size_t mbsrtowcs(wchar_t *restrict _dst_ , const char **restrict _src_ ,
               size_t _len_ , mbstate_t *restrict _ps_);
    


## DESCRIPTION



           For _mbsrtowcs_(): 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.
    
           The _mbsrtowcs_() function shall convert a sequence of characters,
           beginning in the conversion state described by the object pointed
           to by _ps_ , from the array indirectly pointed to by _src_ into a
           sequence of corresponding wide characters. If _dst_ is not a null
           pointer, the converted characters shall be stored into the array
           pointed to by _dst_.  Conversion continues up to and including a
           terminating null character, which shall also be stored. Conversion
           shall stop early in either of the following cases:
    
            *  A sequence of bytes is encountered that does not form a valid
               character.
    
            *  _len_ codes have been stored into the array pointed to by _dst_
               (and _dst_ is not a null pointer).
    
           Each conversion shall take place as if by a call to the _mbrtowc_()
           function.
    
           If _dst_ is not a null pointer, the pointer object pointed to by _src_
           shall be assigned either a null pointer (if conversion stopped due
           to reaching a terminating null character) or the address just past
           the last character converted (if any). If conversion stopped due
           to reaching a terminating null character, and if _dst_ is not a null
           pointer, the resulting state described shall be the initial
           conversion state.
    
           If _ps_ is a null pointer, the _mbsrtowcs_() function shall use its
           own internal **mbstate_t** object, which is 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 _mbsnrtowcs_() function shall be equivalent to the _mbsrtowcs_()
           function, except that the conversion of characters indirectly
           pointed to by _src_ is limited to at most _nmc_ bytes (the size of the
           input buffer), and under conditions where _mbsrtowcs_() would assign
           the address just past the last character converted (if any) to the
           pointer object pointed to by _src_ , _mbsnrtowcs_() shall instead
           assign the address just past the last byte processed (if any) to
           that pointer object. If the input buffer ends with an incomplete
           character, it is unspecified whether conversion stops at the end
           of the previous character (if any), or at the end of the input
           buffer. In the latter case, a subsequent call to _mbsnrtowcs_() with
           an input buffer that starts with the remainder of the incomplete
           character shall correctly complete the conversion of that
           character.
    
           The behavior of these functions shall be affected by the _LC_CTYPE_
           category of the current locale.
    
           The implementation shall behave as if no function defined in this
           volume of POSIX.1‐2017 calls these functions.
    
           The _mbsnrtowcs_() and _mbsrtowcs_() functions need not be thread-safe
           if called with a NULL _ps_ argument.
    
           The _mbsrtowcs_() function shall not change the setting of _errno_ if
           successful.
    


## RETURN VALUE



           If the input conversion encounters a sequence of bytes that do not
           form a valid character, an encoding error occurs. In this case,
           these functions shall store the value of the macro **[EILSEQ]** in
           _errno_ and shall return (**size_t**)-1; the conversion state is
           undefined.  Otherwise, these functions shall return the number of
           characters successfully converted, not including the terminating
           null (if any).
    


## ERRORS



           These functions 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.
    
           These functions 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



           A future version may require that when the input buffer ends with
           an incomplete character, conversion stops at the end of the input
           buffer.
    


* * *