The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> mbtowc - convert a character to a wide-character code

#### SYNOPSIS

> ``#include <stdlib.h>
> int mbtowc(wchar_t *restrict` pwc`, const char *restrict` s`, size_t` n`);
> ``

#### DESCRIPTION

> [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.1-2008 defers to the ISO C standard.

> If s is not a null pointer, mbtowc() shall determine the number of bytes that constitute the character pointed to by s. It shall then determine the wide-character code for the value of type wchar_t that corresponds to that character. (The value of the wide-character code corresponding to the null byte is 0.) If the character is valid and pwc is not a null pointer, mbtowc() shall store the wide-character code in the object pointed to by pwc.

> The behavior of this function is affected by the LC_CTYPE category of the current locale. For a state-dependent encoding, this function is placed into its initial state by a call for which its character pointer argument, s, is a null pointer. Subsequent calls with s as other than a null pointer shall cause the internal state of the function to be altered as necessary. A call with s as a null pointer shall cause this function to return a non-zero value if encodings have state dependency, and 0 otherwise. If the implementation employs special bytes to change the shift state, these bytes shall not produce separate wide-character codes, but shall be grouped with an adjacent character. Changing the LC_CTYPE category causes the shift state of this function to be unspecified. At most n bytes of the array pointed to by s shall be examined.

> The implementation shall behave as if no function defined in this volume of POSIX.1-2008 calls mbtowc().

> [CX] The mbtowc() function need not be thread-safe.

#### RETURN VALUE

> If s is a null pointer, mbtowc() shall return a non-zero or 0 value, if character encodings, respectively, do or do not have state-dependent encodings. If s is not a null pointer, mbtowc() shall either return 0 (if s points to the null byte), or return the number of bytes that constitute the converted character (if the next n or fewer bytes form a valid character), or return -1 [CX] and shall set errno to indicate the error (if they do not form a valid character).

> In no case shall the value returned be greater than n or the value of the {MB_CUR_MAX} macro.

#### ERRORS

> The mbtowc() function shall fail if:

> [EILSEQ]
>   [CX] An invalid character sequence is detected. In the POSIX locale an [EILSEQ] error cannot occur since all byte values are valid characters.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> None.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> mblen, mbstowcs, wctomb, wcstombs

> XBD <stdlib.h>

#### CHANGE HISTORY

> First released in Issue 4. Aligned with the ISO C standard.

#### Issue 6

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

> Extensions beyond the ISO C standard are marked.

#### Issue 7

> Austin Group Interpretation 1003.1-2001 #170 is applied.

> POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0372 [109] and XSH/TC1-2008/0373 [195] are applied.

> POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0209 [663,674] is applied.

End of informative text.

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