The
ungetwc() function pushes the wide-character
wc (converted to an wchar_t) back onto the input stream pointed to by
stream. The pushed-backed wide-characters will be returned by subsequent reads on the stream (in reverse order). A successful intervening call, using the same stream, to one of the file positioning functions
fseek(3),
fsetpos(3), or
rewind(3) will discard the pushed back wide-characters.
One wide-character of push-back is guaranteed, but as long as there is sufficient memory, an effectively infinite amount of pushback is allowed.
If a character is successfully pushed-back, the end-of-file indicator for the stream is cleared.