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 1.12 2001/10/01 16:09:00 ru Exp $
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  39 .Dd June 9, 1993
  40 .Dt STRERROR 3
  41 .Os
  42 .Sh NAME
  43 .Nm perror ,
  44 .Nm strerror ,
  45 .Nm sys_errlist ,
  46 .Nm sys_nerr
  47 .Nd system error messages
  48 .Sh LIBRARY
  49 .Lb libc
  50 .Sh SYNOPSIS
  51 .In stdio.h
  52 .Ft void
  53 .Fn perror "const char *string"
  54 .Vt extern const char * const sys_errlist[] ;
  55 .Vt extern const int sys_nerr ;
  56 .In string.h
  57 .Ft char *
  58 .Fn strerror "int errnum"
  59 .Sh DESCRIPTION
  60 The
  61 .Fn strerror
  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
  72 returns a pointer to the corresponding
  73 message string.
  74 .Pp
  75 The
  76 .Fn perror
  77 function finds the error message corresponding to the current
  78 value of the global variable
  79 .Va errno
  80 .Pq Xr intro 2
  81 and writes it, followed by a newline, to the
  82 standard error file descriptor.
  83 If the argument
  84 .Fa string
  85 is
  86 .Pf non- Dv NULL
  87 and does not point to the null character,
  88 this string is prepended to the message
  89 string and separated from it by
  90 a colon and space
  91 .Pq Ql \&:\ \& ;
  92 otherwise, only the error message string is printed.
  93 .Pp
  94 If
  95 .Fa errnum
  96 is not a recognized error number,
  97 the error message string will contain
  98 .Dq Li "Unknown error:\ "
  99 followed by the error number in decimal.
 100 .Pp
 101 The message strings can be accessed directly using the external
 102 array
 103 .Va sys_errlist .
 104 The external value
 105 .Va sys_nerr
 106 contains a count of the messages in
 107 .Va sys_errlist .
 108 The use of these variables is deprecated;
 109 .Fn strerror
 110 should be used instead.
 111 .Sh SEE ALSO
 112 .Xr intro 2 ,
 113 .Xr psignal 3
 114 .Sh HISTORY
 115 The
 116 .Fn strerror
 117 and
 118 .Fn perror
 119 functions first appeared in
 120 .Bx 4.4 .
 121 .Sh BUGS
 122 For unknown error numbers, the
 123 .Fn strerror
 124 function will return its result in a static buffer which
 125 may be overwritten by subsequent calls.
 126 .Pp
 127 Programs that use the deprecated
 128 .Va sys_errlist
 129 variable often fail to compile because they declare it
 130 inconsistently.