c/string/multibyte/c32rtomb

Converts a single code point from its variable-length 32-bit wide character representation (but typically, UTF-32) to its narrow multibyte character representation.

If is not a null pointer, the function determines the number of bytes necessary to store the multibyte character representation of  (including any shift sequences, and taking into account the current multibyte conversion state ), and stores the multibyte character representation in the character array whose first element is pointed to by,  updating  as necessary. At most bytes can be written by this function.

If is a null pointer, the call is equivalent to  for some internal buffer.

If is the null wide character, a null byte is stored, preceded by any shift sequence necessary to restore the initial shift state and the conversion state parameter  is updated to represent the initial shift state.

If the macro is defined, the 32-bit encoding used by this function is UTF-32; otherwise, it is implementation-defined. In any case, the multibyte character encoding used by this function is specified by the currently active C locale.

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. This value may be, e.g. when processing the leading units in a multi--unit sequence (does not occur in UTF-32).

On failure (if is not a valid 32-bit wide character), returns, stores eilseq in errno, and leaves  in unspecified state.