string/FreeBSD/strerror.3

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  36 .\"     @(#)strerror.3  8.1 (Berkeley) 6/9/93
  37 .\" $FreeBSD: src/lib/libc/string/strerror.3,v 1.22 2002/12/19 10:24:52 tjr Exp $
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  39 .Dd December 19, 2002
  40 .Dt STRERROR 3
  41 .Os
  42 .Sh NAME
  43 .Nm perror ,
  44 .Nm strerror ,
  45 .Nm strerror_r ,
  46 .Nm sys_errlist ,
  47 .Nm sys_nerr
  48 .Nd system error messages
  49 .Sh LIBRARY
  50 .Lb libc
  51 .Sh SYNOPSIS
  52 .In stdio.h
  53 .Ft void
  54 .Fn perror "const char *string"
  55 .Vt extern const char * const sys_errlist[] ;
  56 .Vt extern const int sys_nerr ;
  57 .In string.h
  58 .Ft "char *"
  59 .Fn strerror "int errnum"
  60 .Ft int
  61 .Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
  62 .Sh DESCRIPTION
  63 The
  64 .Fn strerror ,
  65 .Fn strerror_r
  66 and
  67 .Fn perror
  68 functions look up the error message string corresponding to an
  69 error number.
  70 .Pp
  71 The
  72 .Fn strerror
  73 function accepts an error number argument
  74 .Fa errnum
  75 and returns a pointer to the corresponding
  76 message string.
  77 .Pp
  78 The
  79 .Fn strerror_r
  80 function renders the same result into
  81 .Fa strerrbuf
  82 for a maximum of
  83 .Fa buflen
  84 characters and returns 0 upon success.
  85 .Pp
  86 The
  87 .Fn perror
  88 function finds the error message corresponding to the current
  89 value of the global variable
  90 .Va errno
  91 .Pq Xr intro 2
  92 and writes it, followed by a newline, to the
  93 standard error file descriptor.
  94 If the argument
  95 .Fa string
  96 is
  97 .Pf non- Dv NULL
  98 and does not point to the null character,
  99 this string is prepended to the message
 100 string and separated from it by
 101 a colon and space
 102 .Pq Dq Li ":\ " ;
 103 otherwise, only the error message string is printed.
 104 .Pp
 105 If
 106 .Fa errnum
 107 is not a recognized error number,
 108 .Fn strerror
 109 returns an error message string containing
 110 .Dq Li "Unknown error:\ "
 111 followed by the error number in decimal, while
 112 .Fn strerror_r
 113 leaves
 114 .Fa strerrbuf
 115 unchanged and returns
 116 .Er EINVAL .
 117 Error numbers recognized by this implementation fall in
 118 the range 0 <
 119 .Fa errnum
 120 <
 121 .Fa sys_nerr .
 122 .Pp
 123 If insufficient storage is provided in
 124 .Fa strerrbuf
 125 (as specified in
 126 .Fa buflen )
 127 to contain the error string,
 128 .Fn strerror_r
 129 returns
 130 .Er ERANGE
 131 and
 132 .Fa strerrbuf
 133 will contain an error message that has been truncated and
 134 .Dv NUL
 135 terminated to fit the length specified by
 136 .Fa buflen .
 137 .Pp
 138 The message strings can be accessed directly using the external
 139 array
 140 .Va sys_errlist .
 141 The external value
 142 .Va sys_nerr
 143 contains a count of the messages in
 144 .Va sys_errlist .
 145 The use of these variables is deprecated;
 146 .Fn strerror
 147 or
 148 .Fn strerror_r
 149 should be used instead.
 150 .Sh SEE ALSO
 151 .Xr intro 2 ,
 152 .Xr psignal 3
 153 .Sh STANDARDS
 154 The
 155 .Fn perror
 156 and
 157 .Fn strerror
 158 functions conform to
 159 .St -isoC-99 .
 160 The
 161 .Fn strerror_r
 162 function conforms to
 163 .St -p1003.1-2001 .
 164 .Sh HISTORY
 165 The
 166 .Fn strerror
 167 and
 168 .Fn perror
 169 functions first appeared in
 170 .Bx 4.4 .
 171 The
 172 .Fn strerror_r
 173 function was implemented in
 174 .Fx 4.4
 175 by
 176 .An Wes Peters Aq wes@FreeBSD.org .
 177 .Sh BUGS
 178 For unknown error numbers, the
 179 .Fn strerror
 180 function will return its result in a static buffer which
 181 may be overwritten by subsequent calls.
 182 .Pp
 183 The return type for
 184 .Fn strerror
 185 is missing a type-qualifier; it should actually be
 186 .Vt const char * .
 187 .Pp
 188 Programs that use the deprecated
 189 .Va sys_errlist
 190 variable often fail to compile because they declare it
 191 inconsistently.