Synopsis

#include <stdlib.h>

int mbtowc(wchar_t *restrict pwc, const char *restrict s, size_t n);

Status

Partially implemented

Conformance

IEEE Std 1003.1-2017

Description

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.1-2017 calls mbtowc().

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

Tests

Untested

Known bugs

None

See Also

  1. Standard library functions
  2. Table of Contents