std::wcrtomb (3) - Linux Man Pages
Defined in header <cwchar>
std::size_t wcrtomb( char* s, wchar_t wc, std::mbstate_t* ps );
Converts a wide character to its narrow multibyte representation.
If s is not a null pointer, the function determines the number of bytes necessary to store the multibyte character representation of wc (including any shift sequences, and taking into account the current multibyte conversion state *ps), and stores the multibyte character representation in the character array whose first element is pointed to by s, updating *ps as necessary. At most MB_CUR_MAX bytes can be written by this function.
If s is a null pointer, the call is equivalent to std::wcrtomb(buf, L'\0', ps) for some internal buffer buf.
If wc is the null wide character L'\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.
s - pointer to narrow character array where the multibyte character will be stored
wc - the wide character to convert
ps - pointer to the conversion state object used when interpreting the multibyte string
On success, returns the number of bytes (including any shift sequences) written to the character array whose first element is pointed to by s.
On failure (if wc is not a valid wide character), returns static_cast<std::size_t>(-1), stores EILSEQ in errno, and leaves *ps in unspecified state.
// Run this code
do_out converts a string from internT to externT, such as when writing to file