stdio/ungetc.3

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  36 .\"     @(#)ungetc.3    8.1 (Berkeley) 6/4/93
  37 .\" $FreeBSD: src/lib/libc/stdio/ungetc.3,v 1.13 2002/10/10 04:12:40 tjr Exp $
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  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 .In stdio.h
  49 .Ft int
  50 .Fo ungetc
  51 .Fa "int c"
  52 .Fa "FILE *stream"
  53 .Fc
  54 .Sh DESCRIPTION
  55 The
  56 .Fn ungetc
  57 function pushes the character
  58 .Fa c
  59 (converted to an unsigned char)
  60 back onto the input stream pointed to by
  61 .Fa stream .
  62 The pushed-back characters will be returned (in reverse order)
  63 by subsequent reads on the stream.
  64 A successful intervening call
  65 to one of the file positioning functions
  66 .Xr ( fseek 3 ,
  67 .Xr fsetpos 3 ,
  68 or
  69 .Xr rewind 3 ) ,
  70 using the same stream,
  71 will discard the pushed-back characters.
  72 .Pp
  73 Only one character of push-back is guaranteed,
  74 but as long as there is sufficient memory,
  75 an effectively infinite amount of push-back is allowed.
  76 .Pp
  77 If a character is successfully pushed-back,
  78 the end-of-file indicator for the stream is cleared.
  79 The file-position indicator is decremented
  80 by each successful call to
  81 .Fn ungetc ;
  82 if its value was 0 before a call, its value is unspecified after
  83 the call.
  84 .Sh RETURN VALUES
  85 The
  86 .Fn ungetc
  87 function returns the character pushed-back after the conversion,
  88 or
  89 .Dv EOF
  90 if the operation fails.
  91 If the value of the argument
  92 .Fa c
  93 character equals
  94 .Dv EOF ,
  95 the operation will fail and the stream will remain unchanged.
  96 .Sh SEE ALSO
  97 .Xr fseek 3 ,
  98 .Xr getc 3 ,
  99 .Xr setvbuf 3 ,
 100 .Xr ungetwc 3
 101 .Sh STANDARDS
 102 The
 103 .Fn ungetc
 104 function conforms to
 105 .St -isoC .