V7/usr/man/man3/ungetc.3s

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.TH UNGETC 3S 
.SH NAME
ungetc \- push character back into input stream
.SH SYNOPSIS
.B #include <stdio.h>
.PP
.B ungetc(c, stream)
.br
.SM
.B FILE
.B *stream;
.SH DESCRIPTION
.I Ungetc
pushes the character
.I c
back on an input stream.
That character will be returned by the next
.I getc
call on that stream.
.I Ungetc 
returns 
.IR c .
.PP
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.
.PP
.IR  Fseek (3)
erases all memory of pushed back characters.
.SH "SEE ALSO"
getc(3), setbuf(3), fseek(3)
.SH DIAGNOSTICS
.I Ungetc
returns
.SM
.B EOF
if it can't push a character back.