NAME

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

SYNOPSIS

#include <wchar.h>



[CX] 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(): ^[CX]  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.1-2024 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.

^[CX] 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, conversion shall stop at the end of the input buffer; 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.1-2024 calls these functions.

^[CX] If called with a null ps argument, the mbsnrtowcs() function need not be thread-safe; however, such calls shall avoid data races with calls to mbsnrtowcs() with a non-null argument and with calls to all other functions.

If called with a null ps argument, the mbsrtowcs() function need not be thread-safe; however, such calls shall avoid data races with calls to mbsrtowcs() with a non-null argument and with calls to all other functions.

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. ^[CX]  In the POSIX locale an [EILSEQ] error cannot occur since all byte values are valid characters.

These functions may fail if:

[EINVAL]

^[CX] ps points to an object that contains an invalid conversion state.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

iconv, mbrtowc, mbsinit

XBD <wchar.h>

CHANGE HISTORY

First released in Issue 5. Included for alignment with ISO/IEC 9899:1990/Amendment 1:1995 (E).

Issue 6

The mbsrtowcs() prototype is updated for alignment with the ISO/IEC 9899:1999 standard.

The [EINVAL] error condition is marked CX.

Issue 7

Austin Group Interpretation 1003.1-2001 #170 is applied.

The mbsnrtowcs() function is added from The Open Group Technical Standard, 2006, Extended API Set Part 1.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0370 [109,105] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0205 [601], XSH/TC2-2008/0206 [663], and XSH/TC2-2008/0207 [601] are applied.

Issue 8

Austin Group Defect 616 is applied, requiring that when the mbsnrtowcs() input buffer ends with an incomplete character, conversion stops at the end of the input buffer (not at the end of the previous character, if any).

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.