stdio/FreeBSD/fgets.3

   1 .\" Copyright (c) 1990, 1991, 1993
   2 .\"     The Regents of the University of California.  All rights reserved.
   3 .\"
   4 .\" This code is derived from software contributed to Berkeley by
   5 .\" Chris Torek and the American National Standards Committee X3,
   6 .\" on Information Processing Systems.
   7 .\"
   8 .\" Redistribution and use in source and binary forms, with or without
   9 .\" modification, are permitted provided that the following conditions
  10 .\" are met:
  11 .\" 1. Redistributions of source code must retain the above copyright
  12 .\"    notice, this list of conditions and the following disclaimer.
  13 .\" 2. Redistributions in binary form must reproduce the above copyright
  14 .\"    notice, this list of conditions and the following disclaimer in the
  15 .\"    documentation and/or other materials provided with the distribution.
  16 .\" 3. All advertising materials mentioning features or use of this software
  17 .\"    must display the following acknowledgement:
  18 .\"     This product includes software developed by the University of
  19 .\"     California, Berkeley and its contributors.
  20 .\" 4. Neither the name of the University nor the names of its contributors
  21 .\"    may be used to endorse or promote products derived from this software
  22 .\"    without specific prior written permission.
  23 .\"
  24 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34 .\" SUCH DAMAGE.
  35 .\"
  36 .\"     @(#)fgets.3     8.1 (Berkeley) 6/4/93
  37 .\" $FreeBSD: src/lib/libc/stdio/fgets.3,v 1.19 2002/12/04 18:57:45 ru Exp $
  38 .\"
  39 .Dd June 4, 1993
  40 .Dt FGETS 3
  41 .Os
  42 .Sh NAME
  43 .Nm fgets ,
  44 .Nm gets
  45 .Nd get a line from a stream
  46 .Sh LIBRARY
  47 .Lb libc
  48 .Sh SYNOPSIS
  49 .In stdio.h
  50 .Ft char *
  51 .Fn fgets "char * restrict str" "int size" "FILE * restrict stream"
  52 .Ft char *
  53 .Fn gets "char *str"
  54 .Sh DESCRIPTION
  55 The
  56 .Fn fgets
  57 function
  58 reads at most one less than the number of characters specified by
  59 .Fa size
  60 from the given
  61 .Fa stream
  62 and stores them in the string
  63 .Fa str .
  64 Reading stops when a newline character is found,
  65 at end-of-file or error.
  66 The newline, if any, is retained.
  67 If any characters are read and there is no error, a
  68 .Ql \e0
  69 character is appended to end the string.
  70 .Pp
  71 The
  72 .Fn gets
  73 function
  74 is equivalent to
  75 .Fn fgets
  76 with an infinite
  77 .Fa size
  78 and a
  79 .Fa stream
  80 of
  81 .Dv stdin ,
  82 except that the newline character (if any) is not stored in the string.
  83 It is the caller's responsibility to ensure that the input line,
  84 if any, is sufficiently short to fit in the string.
  85 .Sh RETURN VALUES
  86 Upon successful completion,
  87 .Fn fgets
  88 and
  89 .Fn gets
  90 return
  91 a pointer to the string.
  92 If end-of-file occurs before any characters are read,
  93 they return
  94 .Dv NULL
  95 and the buffer contents remain unchanged.
  96 If an error occurs,
  97 they return
  98 .Dv NULL
  99 and the buffer contents are indeterminate.
 100 The
 101 .Fn fgets
 102 and
 103 .Fn gets
 104 functions
 105 do not distinguish between end-of-file and error, and callers must use
 106 .Xr feof 3
 107 and
 108 .Xr ferror 3
 109 to determine which occurred.
 110 .Sh ERRORS
 111 .Bl -tag -width Er
 112 .It Bq Er EBADF
 113 The given
 114 .Fa stream
 115 is not a readable stream.
 116 .El
 117 .Pp
 118 The function
 119 .Fn fgets
 120 may also fail and set
 121 .Va errno
 122 for any of the errors specified for the routines
 123 .Xr fflush 3 ,
 124 .Xr fstat 2 ,
 125 .Xr read 2 ,
 126 or
 127 .Xr malloc 3 .
 128 .Pp
 129 The function
 130 .Fn gets
 131 may also fail and set
 132 .Va errno
 133 for any of the errors specified for the routine
 134 .Xr getchar 3 .
 135 .Sh SECURITY CONSIDERATIONS
 136 The
 137 .Fn gets
 138 function cannot be used securely.
 139 Because of its lack of bounds checking,
 140 and the inability for the calling program
 141 to reliably determine the length of the next incoming line,
 142 the use of this function enables malicious users
 143 to arbitrarily change a running program's functionality through
 144 a buffer overflow attack.
 145 It is strongly suggested that the
 146 .Fn fgets
 147 function be used in all cases.
 148 (See
 149 the FSA.)
 150 .Sh SEE ALSO
 151 .Xr feof 3 ,
 152 .Xr ferror 3 ,
 153 .Xr fgetln 3 ,
 154 .Xr fgetws 3
 155 .Rs
 156 .%T "The FreeBSD Security Architecture"
 157 .Re
 158 (See
 159 .Pa /usr/share/doc/{to be determined} . )
 160 .Sh STANDARDS
 161 The functions
 162 .Fn fgets
 163 and
 164 .Fn gets
 165 conform to
 166 .St -isoC-99 .