xref: /freebsd/lib/libc/stdio/ungetc.3 (revision 6990ffd8a95caaba6858ad44ff1b3157d1efba8f)
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36.\"     @(#)ungetc.3	8.1 (Berkeley) 6/4/93
37.\" $FreeBSD$
38.\"
39.Dd June 4, 1993
40.Dt UNGETC 3
41.Os
42.Sh NAME
43.Nm ungetc
44.Nd un-get character from input stream
45.Sh LIBRARY
46.Lb libc
47.Sh SYNOPSIS
48.Fd #include <stdio.h>
49.Ft int
50.Fn ungetc "int c" "FILE *stream"
51.Sh DESCRIPTION
52The
53.Fn ungetc
54function pushes the character
55.Fa c
56(converted to an unsigned char)
57back onto the input stream pointed to by
58.Fa stream .
59The pushed-back characters will be returned by subsequent reads on the
60stream (in reverse order).
61A successful intervening call,
62using the same stream,
63to one of the file positioning functions
64.Xr ( fseek 3 ,
65.Xr fsetpos 3 ,
66or
67.Xr rewind 3 )
68will discard the pushed back characters.
69.Pp
70One character of push-back is guaranteed,
71but as long as there is sufficient memory,
72an effectively infinite amount of pushback is allowed.
73.Pp
74If a character is successfully pushed-back,
75the end-of-file indicator for the stream is cleared.
76The file-position indicator is decremented
77by each successful call to
78.Fn ungetc ;
79if its value was 0 before a call, its value is unspecified after
80the call.
81.Sh RETURN VALUES
82The
83.Fn ungetc
84function returns the character pushed-back after the conversion,
85or
86.Dv EOF
87if the operation fails.
88If the value of the argument
89.Fa c
90character equals
91.Dv EOF ,
92the operation will fail and the stream will remain unchanged.
93.Sh SEE ALSO
94.Xr fseek 3 ,
95.Xr getc 3 ,
96.Xr setvbuf 3
97.Sh STANDARDS
98The
99.Fn ungetc
100function conforms to
101.St -isoC .
102