stdio/ungetc.3

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  32 .\"     @(#)ungetc.3    8.1 (Berkeley) 6/4/93
  33 .\" $FreeBSD: src/lib/libc/stdio/ungetc.3,v 1.14 2007/01/09 00:28:07 imp Exp $
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  35 .Dd June 4, 1993
  36 .Dt UNGETC 3
  37 .Os
  38 .Sh NAME
  39 .Nm ungetc
  40 .Nd un-get character from input stream
  41 .Sh LIBRARY
  42 .Lb libc
  43 .Sh SYNOPSIS
  44 .In stdio.h
  45 .Ft int
  46 .Fo ungetc
  47 .Fa "int c"
  48 .Fa "FILE *stream"
  49 .Fc
  50 .Sh DESCRIPTION
  51 The
  52 .Fn ungetc
  53 function pushes the character
  54 .Fa c
  55 (converted to an unsigned char)
  56 back onto the input stream pointed to by
  57 .Fa stream .
  58 The pushed-back characters will be returned (in reverse order)
  59 by subsequent reads on the stream.
  60 A successful intervening call
  61 to one of the file positioning functions
  62 .Xr ( fseek 3 ,
  63 .Xr fsetpos 3 ,
  64 or
  65 .Xr rewind 3 ) ,
  66 using the same stream,
  67 will discard the pushed-back characters.
  68 .Pp
  69 Only one character of push-back is guaranteed,
  70 but as long as there is sufficient memory,
  71 an effectively infinite amount of push-back is allowed.
  72 .Pp
  73 If a character is successfully pushed-back,
  74 the end-of-file indicator for the stream is cleared.
  75 The file-position indicator is decremented
  76 by each successful call to
  77 .Fn ungetc ;
  78 if its value was 0 before a call, its value is unspecified after
  79 the call.
  80 .Sh RETURN VALUES
  81 The
  82 .Fn ungetc
  83 function returns the character pushed-back after the conversion,
  84 or
  85 .Dv EOF
  86 if the operation fails.
  87 If the value of the argument
  88 .Fa c
  89 character equals
  90 .Dv EOF ,
  91 the operation will fail and the stream will remain unchanged.
  92 .Sh SEE ALSO
  93 .Xr fseek 3 ,
  94 .Xr getc 3 ,
  95 .Xr setvbuf 3 ,
  96 .Xr ungetwc 3
  97 .Sh STANDARDS
  98 The
  99 .Fn ungetc
 100 function conforms to
 101 .St -isoC .