std::ungetwc

std::wint_t ungetwc( std::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 std::ungetwc.

If std::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 std::ungetwc were performed, read operations retrieve the pushed-back wide characters in reverse order of std::ungetwc

If ch equals WEOF, the operation fails and the stream is not affected.

A successful call to std::ungetwc clears the end of file status flag feof.

A successful call to std::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 std::ungetwc.

Parameters

Return value

On success ch is returned.

On failure WEOF is returned and the given stream remains unchanged.

See also