string/strerror.3

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  36 .\"     @(#)strerror.3  8.1 (Berkeley) 6/9/93
  37 .\" $FreeBSD: src/lib/libc/string/strerror.3,v 1.23 2004/10/12 14:52:52 keramida Exp $
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  39 .Dd October 12, 2004
  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 .Fo perror
  55 .Fa "const char *s"
  56 .Fc
  57 .Vt extern const char * const sys_errlist[] ;
  58 .Vt extern const int sys_nerr ;
  59 .In string.h
  60 .Ft "char *"
  61 .Fo strerror
  62 .Fa "int errnum"
  63 .Fc
  64 .Ft int
  65 .Fo strerror_r
  66 .Fa "int errnum"
  67 .Fa "char *strerrbuf"
  68 .Fa "size_t buflen"
  69 .Fc
  70 .Sh DESCRIPTION
  71 The
  72 .Fn strerror ,
  73 .Fn strerror_r ,
  74 and
  75 .Fn perror
  76 functions look up the error message string corresponding to an
  77 error number.
  78 .Pp
  79 The
  80 .Fn strerror
  81 function accepts an error number argument
  82 .Fa errnum
  83 and returns a pointer to the corresponding
  84 message string.
  85 .Pp
  86 The
  87 .Fn strerror_r
  88 function renders the same result into
  89 .Fa strerrbuf
  90 for a maximum of
  91 .Fa buflen
  92 characters and returns 0 upon success.
  93 .Pp
  94 The
  95 .Fn perror
  96 function finds the error message corresponding to the current
  97 value of the global variable
  98 .Va errno
  99 .Pq Xr intro 2
 100 and writes it, followed by a newline, to the
 101 standard error file descriptor.
 102 If the argument
 103 .Fa s
 104 is
 105 .Pf non- Dv NULL
 106 and does not point to the null character,
 107 this string is prepended to the message
 108 string and separated from it by
 109 a colon and space
 110 .Pq Dq Li ":\ " ;
 111 otherwise, only the error message string is printed.
 112 .Pp
 113 If the error number is not recognized, these functions return an error message
 114 string containing
 115 .Dq Li "Unknown error:\ "
 116 followed by the error number in decimal.
 117 The
 118 .Fn strerror
 119 and
 120 .Fn strerror_r
 121 functions return
 122 .Er EINVAL
 123 as a warning.
 124 Error numbers recognized by this implementation fall in
 125 the range 0 <
 126 .Fa errnum
 127 <
 128 .Fa sys_nerr .
 129 .Pp
 130 If insufficient storage is provided in
 131 .Fa strerrbuf
 132 (as specified in
 133 .Fa buflen )
 134 to contain the error string,
 135 .Fn strerror_r
 136 returns
 137 .Er ERANGE
 138 and
 139 .Fa strerrbuf
 140 will contain an error message that has been truncated and
 141 .Dv NUL
 142 terminated to fit the length specified by
 143 .Fa buflen .
 144 .Pp
 145 The message strings can be accessed directly using the external
 146 array
 147 .Va sys_errlist .
 148 The external value
 149 .Va sys_nerr
 150 contains a count of the messages in
 151 .Va sys_errlist .
 152 The use of these variables is deprecated;
 153 .Fn strerror
 154 or
 155 .Fn strerror_r
 156 should be used instead.
 157 .Sh SEE ALSO
 158 .Xr intro 2 ,
 159 .Xr psignal 3
 160 .Sh STANDARDS
 161 The
 162 .Fn perror
 163 and
 164 .Fn strerror
 165 functions conform to
 166 .St -isoC-99 .
 167 The
 168 .Fn strerror_r
 169 function conforms to
 170 .St -p1003.1-2001 .
 171 .Sh HISTORY
 172 The
 173 .Fn strerror
 174 and
 175 .Fn perror
 176 functions first appeared in
 177 .Bx 4.4 .
 178 The
 179 .Fn strerror_r
 180 function was implemented in
 181 .Fx 4.4
 182 by
 183 .An Wes Peters Aq wes@FreeBSD.org .
 184 .Sh BUGS
 185 For unknown error numbers, the
 186 .Fn strerror
 187 function will return its result in a static buffer which
 188 may be overwritten by subsequent calls.
 189 .Pp
 190 The return type for
 191 .Fn strerror
 192 is missing a type-qualifier; it should actually be
 193 .Vt const char * .
 194 .Pp
 195 Programs that use the deprecated
 196 .Va sys_errlist
 197 variable often fail to compile because they declare it
 198 inconsistently.