ungetc(3s)
NAME
ungetc − push character back into input stream
SYNTAX
#include <stdio.h>
ungetc(c, stream)
FILE *stream;
DESCRIPTION
The ungetc routine pushes the character c back on an input stream. That character will be returned by the next getc call on that stream. The ungetc routine returns c.
One character of pushback is guaranteed provided something has been read from the stream and the stream is actually buffered. Attempts to push EOF are rejected.
The fseek(3s) routine erases all memory of pushed back characters.
DIAGNOSTICS
The ungetc routine returns EOF if it can’t push a character back.