stdio/FreeBSD/fgets.3

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  32 .\"     @(#)fgets.3     8.1 (Berkeley) 6/4/93
  33 .\" $FreeBSD: src/lib/libc/stdio/fgets.3,v 1.22 2009/02/28 06:00:58 das Exp $
  34 .\"
  35 .Dd June 4, 1993
  36 .Dt FGETS 3
  37 .Os
  38 .Sh NAME
  39 .Nm fgets ,
  40 .Nm gets
  41 .Nd get a line from a stream
  42 .Sh LIBRARY
  43 .Lb libc
  44 .Sh SYNOPSIS
  45 .In stdio.h
  46 .Ft char *
  47 .Fn fgets "char * restrict str" "int size" "FILE * restrict stream"
  48 .Ft char *
  49 .Fn gets "char *str"
  50 .Sh DESCRIPTION
  51 The
  52 .Fn fgets
  53 function
  54 reads at most one less than the number of characters specified by
  55 .Fa size
  56 from the given
  57 .Fa stream
  58 and stores them in the string
  59 .Fa str .
  60 Reading stops when a newline character is found,
  61 at end-of-file or error.
  62 The newline, if any, is retained.
  63 If any characters are read and there is no error, a
  64 .Ql \e0
  65 character is appended to end the string.
  66 .Pp
  67 The
  68 .Fn gets
  69 function
  70 is equivalent to
  71 .Fn fgets
  72 with an infinite
  73 .Fa size
  74 and a
  75 .Fa stream
  76 of
  77 .Dv stdin ,
  78 except that the newline character (if any) is not stored in the string.
  79 It is the caller's responsibility to ensure that the input line,
  80 if any, is sufficiently short to fit in the string.
  81 .Sh RETURN VALUES
  82 Upon successful completion,
  83 .Fn fgets
  84 and
  85 .Fn gets
  86 return
  87 a pointer to the string.
  88 If end-of-file occurs before any characters are read,
  89 they return
  90 .Dv NULL
  91 and the buffer contents remain unchanged.
  92 If an error occurs,
  93 they return
  94 .Dv NULL
  95 and the buffer contents are indeterminate.
  96 The
  97 .Fn fgets
  98 and
  99 .Fn gets
 100 functions
 101 do not distinguish between end-of-file and error, and callers must use
 102 .Xr feof 3
 103 and
 104 .Xr ferror 3
 105 to determine which occurred.
 106 .Sh ERRORS
 107 .Bl -tag -width Er
 108 .It Bq Er EBADF
 109 The given
 110 .Fa stream
 111 is not a readable stream.
 112 .El
 113 .Pp
 114 The function
 115 .Fn fgets
 116 may also fail and set
 117 .Va errno
 118 for any of the errors specified for the routines
 119 .Xr fflush 3 ,
 120 .Xr fstat 2 ,
 121 .Xr read 2 ,
 122 or
 123 .Xr malloc 3 .
 124 .Pp
 125 The function
 126 .Fn gets
 127 may also fail and set
 128 .Va errno
 129 for any of the errors specified for the routine
 130 .Xr getchar 3 .
 131 .Sh SECURITY CONSIDERATIONS
 132 The
 133 .Fn gets
 134 function cannot be used securely.
 135 Because of its lack of bounds checking,
 136 and the inability for the calling program
 137 to reliably determine the length of the next incoming line,
 138 the use of this function enables malicious users
 139 to arbitrarily change a running program's functionality through
 140 a buffer overflow attack.
 141 It is strongly suggested that the
 142 .Fn fgets
 143 function be used in all cases.
 144 (See
 145 the FSA.)
 146 .Sh SEE ALSO
 147 .Xr feof 3 ,
 148 .Xr ferror 3 ,
 149 .Xr fgetln 3 ,
 150 .Xr fgetws 3 ,
 151 .Xr getline 3
 152 .Sh STANDARDS
 153 The functions
 154 .Fn fgets
 155 and
 156 .Fn gets
 157 conform to
 158 .St -isoC-99 .