xref: /freebsd/lib/libc/stdio/ungetc.3 (revision fbbd9655e5107c68e4e0146ff22b73d7350475bc)

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.\"     @(#)ungetc.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd June 4, 1993
.Dt UNGETC 3
.Os
.Sh NAME
.Nm ungetc
.Nd un-get character from input stream
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft int
.Fn ungetc "int c" "FILE *stream"
.Sh DESCRIPTION
The
.Fn ungetc
function pushes the character
.Fa c
(converted to an unsigned char)
back onto the input stream pointed to by
.Fa 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
.Xr ( fseek 3 ,
.Xr fsetpos 3 ,
or
.Xr rewind 3 )
will discard the pushed back characters.
.Pp
One character of push-back is guaranteed,
but as long as there is sufficient memory,
an effectively infinite amount of pushback is allowed.
.Pp
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
.Fn ungetc ;
if its value was 0 before a call, its value is unspecified after
the call.
.Sh RETURN VALUES
The
.Fn ungetc
function returns the character pushed-back after the conversion,
or
.Dv EOF
if the operation fails.
If the value of the argument
.Fa c
character equals
.Dv EOF ,
the operation will fail and the stream will remain unchanged.
.Sh SEE ALSO
.Xr fseek 3 ,
.Xr getc 3 ,
.Xr setvbuf 3 ,
.Xr ungetwc 3
.Sh STANDARDS
The
.Fn ungetc
function conforms to
.St -isoC .