std::ungetwc (3) - Linux Man Pages
Defined in header <cwchar>
wint_t ungetwc( wint_t ch, std::FILE* stream );
If ch does not equal WEOF, pushes the wide character ch into the input buffer associated with the stream stream in such a manner than subsequent read operation from stream will retrieve that wide character. The external device associated with the stream is not modified.
Stream repositioning operations std::fseek, std::fsetpos, and std::rewind discard the effects of ungetwc.
If ungetwc is called more than once without an intervening read or repositioning, it may fail (in other words, a pushback buffer of size 1 is guaranteed, but any larger buffer is implementation-defined). If multiple successful ungetwc were performed, read operations retrieve the pushed-back wide characters in reverse order of ungetwc
If ch equals WEOF, the operation fails and the stream is not affected.
A successful call to ungetwc clears the end of file status flag feof.
A successful call to ungetwc on a stream (whether text or binary) modifies the stream position indicator in unspecified manner but guarantees that after all pushed-back wide characters are retrieved with a read operation, the stream position indicator is equal to its value before ungetwc.
ch - wide character to be put back
stream - file stream to put the wide character back to
On success ch is returned.
On failure WEOF is returned and the given stream remains unchanged.