The
ungetc()
function pushes the character
c
(converted to an unsigned char)
back onto the input stream pointed to by
stream.
The pushed-back 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 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.
The file-position indicator is decremented
by each successful call to
ungetc();
if its value was 0 before a call, its value is unspecified after
the call.
