c16rtomb
| Defined in header <uchar.h>
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| (since C11) | ||
Converts a single code point from its variable-length 16-bit wide character representation (typically, UTF-16) to its narrow multibyte character representation.
If s is not a null pointer and c16 is the last 16-bit code unit in a valid variable-length encoding of a code point, the function determines the number of bytes necessary to store the multibyte character representation of that code point (including any shift sequences), and stores the multibyte character representation in the character array whose first element is pointed to by s. At most MB_CUR_MAX bytes can be written by this function.
If s is a null pointer, the call is equivalent to c16rtomb(buf, u'\0', ps) for some internal buffer buf.
If c16 is the null wide character u'\0', a null byte is stored, preceded by any shift sequence necessary to restore the initial shift state and the conversion state parameter *ps is updated to represent the initial shift state.
If c16 is not the final code unit in a 16-bit representation of a wide character, it does not write to the array pointed to by s, only *ps is updated.
If the macro __STDC_UTF_16__ is defined, the 16-bit encoding used by this function is UTF-16; otherwise, it is implementation-defined. In any case, the multibyte character encoding used by this function is specified by the currently active C locale.
Parameters
| s | - | pointer to narrow character array where the multibyte character will be stored |
| c16 | - | the 16-bit wide character to convert |
| ps | - | pointer to the conversion state object used when interpreting the multibyte string |
Return value
On success, returns the number of bytes (including any shift sequences) written to the character array whose first element is pointed to by s. This value may be 0, e.g. when processing the leading char16_t units in a multi-char16_t-unit sequence (occurs when processing the leading surrogate in a surrogate pair of UTF-16).
On failure (if c16 is not a valid 16-bit code unit), returns -1, stores EILSEQ in errno, and leaves *ps in unspecified state.
Notes
In C11 as published, unlike mbrtoc16, which converts variable-width multibyte (such as UTF-8) to variable-width 16-bit (such as UTF-16) encoding, this function can only convert single-unit 16-bit encoding, meaning it cannot convert UTF-16 to UTF-8 despite that being the original intent of this function. This was corrected by the post-C11 defect report DR488.