un-get character from input
function pushes the character c (converted to an
unsigned char) back onto the input stream pointed to
by stream. The pushed-backed 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
rewind(3)) will discard the pushed back characters.
One 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.
ungetc() function returns the
character pushed-back after the conversion, or
if the operation fails. If the value of the argument c
EOF, the operation will fail and
the stream will remain unchanged.
fseek(3), getc(3), setvbuf(3)
ungetc() function conforms to
ungetc() function first appeared in
Version 7 AT&T UNIX.