string/FreeBSD/strerror.3

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  32 .\"     @(#)strerror.3  8.1 (Berkeley) 6/9/93
  33 .\" $FreeBSD: src/lib/libc/string/strerror.3,v 1.24 2007/01/09 00:28:12 imp Exp $
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  35 .Dd October 12, 2004
  36 .Dt STRERROR 3
  37 .Os
  38 .Sh NAME
  39 .Nm perror ,
  40 .Nm strerror ,
  41 .Nm strerror_r ,
  42 .Nm sys_errlist ,
  43 .Nm sys_nerr
  44 .Nd system error messages
  45 .Sh LIBRARY
  46 .Lb libc
  47 .Sh SYNOPSIS
  48 .In stdio.h
  49 .Ft void
  50 .Fn perror "const char *string"
  51 .Vt extern const char * const sys_errlist[] ;
  52 .Vt extern const int sys_nerr ;
  53 .In string.h
  54 .Ft "char *"
  55 .Fn strerror "int errnum"
  56 .Ft int
  57 .Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
  58 .Sh DESCRIPTION
  59 The
  60 .Fn strerror ,
  61 .Fn strerror_r
  62 and
  63 .Fn perror
  64 functions look up the error message string corresponding to an
  65 error number.
  66 .Pp
  67 The
  68 .Fn strerror
  69 function accepts an error number argument
  70 .Fa errnum
  71 and returns a pointer to the corresponding
  72 message string.
  73 .Pp
  74 The
  75 .Fn strerror_r
  76 function renders the same result into
  77 .Fa strerrbuf
  78 for a maximum of
  79 .Fa buflen
  80 characters and returns 0 upon success.
  81 .Pp
  82 The
  83 .Fn perror
  84 function finds the error message corresponding to the current
  85 value of the global variable
  86 .Va errno
  87 .Pq Xr intro 2
  88 and writes it, followed by a newline, to the
  89 standard error file descriptor.
  90 If the argument
  91 .Fa string
  92 is
  93 .Pf non- Dv NULL
  94 and does not point to the null character,
  95 this string is prepended to the message
  96 string and separated from it by
  97 a colon and space
  98 .Pq Dq Li ":\ " ;
  99 otherwise, only the error message string is printed.
 100 .Pp
 101 If the error number is not recognized, these functions return an error message
 102 string containing
 103 .Dq Li "Unknown error:\ "
 104 followed by the error number in decimal.
 105 The
 106 .Fn strerror
 107 and
 108 .Fn strerror_r
 109 functions return
 110 .Er EINVAL
 111 as a warning.
 112 Error numbers recognized by this implementation fall in
 113 the range 0 <
 114 .Fa errnum
 115 <
 116 .Fa sys_nerr .
 117 .Pp
 118 If insufficient storage is provided in
 119 .Fa strerrbuf
 120 (as specified in
 121 .Fa buflen )
 122 to contain the error string,
 123 .Fn strerror_r
 124 returns
 125 .Er ERANGE
 126 and
 127 .Fa strerrbuf
 128 will contain an error message that has been truncated and
 129 .Dv NUL
 130 terminated to fit the length specified by
 131 .Fa buflen .
 132 .Pp
 133 The message strings can be accessed directly using the external
 134 array
 135 .Va sys_errlist .
 136 The external value
 137 .Va sys_nerr
 138 contains a count of the messages in
 139 .Va sys_errlist .
 140 The use of these variables is deprecated;
 141 .Fn strerror
 142 or
 143 .Fn strerror_r
 144 should be used instead.
 145 .Sh SEE ALSO
 146 .Xr intro 2 ,
 147 .Xr psignal 3
 148 .Sh STANDARDS
 149 The
 150 .Fn perror
 151 and
 152 .Fn strerror
 153 functions conform to
 154 .St -isoC-99 .
 155 The
 156 .Fn strerror_r
 157 function conforms to
 158 .St -p1003.1-2001 .
 159 .Sh HISTORY
 160 The
 161 .Fn strerror
 162 and
 163 .Fn perror
 164 functions first appeared in
 165 .Bx 4.4 .
 166 The
 167 .Fn strerror_r
 168 function was implemented in
 169 .Fx 4.4
 170 by
 171 .An Wes Peters Aq wes@FreeBSD.org .
 172 .Sh BUGS
 173 For unknown error numbers, the
 174 .Fn strerror
 175 function will return its result in a static buffer which
 176 may be overwritten by subsequent calls.
 177 .Pp
 178 The return type for
 179 .Fn strerror
 180 is missing a type-qualifier; it should actually be
 181 .Vt const char * .
 182 .Pp
 183 Programs that use the deprecated
 184 .Va sys_errlist
 185 variable often fail to compile because they declare it
 186 inconsistently.