man3/strerror.3

   1 .\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright (C) 2005, Michael Kerrisk <mtk-manpages@gmx.net>
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  24 .\" References consulted:
  25 .\"     Linux libc source code
  26 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  27 .\"     386BSD man pages
  28 .\" Modified Sat Jul 24 18:05:30 1993 by Rik Faith <faith@cs.unc.edu>
  29 .\" Modified Fri Feb 16 14:25:17 1996 by Andries Brouwer <aeb@cwi.nl>
  30 .\" Modified Sun Jul 21 20:55:44 1996 by Andries Brouwer <aeb@cwi.nl>
  31 .\" Modified Mon Oct 15 21:16:25 2001 by John Levon <moz@compsoc.man.ac.uk>
  32 .\" Modified Tue Oct 16 00:04:43 2001 by Andries Brouwer <aeb@cwi.nl>
  33 .\" Modified Fri Jun 20 03:04:30 2003 by Andries Brouwer <aeb@cwi.nl>
  34 .\" 2005-12-13, mtk, Substantial rewrite of strerror_r() description
  35 .\"         Addition of extra material on portability and standards.
  36 .\"
  37 .TH STRERROR 3  2005-12-13 "" "Linux Programmer's Manual"
  38 .SH NAME
  39 strerror, strerror_r \- return string describing error number
  40 .SH SYNOPSIS
  41 .nf
  42 .B #include <string.h>
  43 .sp
  44 .BI "char *strerror(int " errnum );
  45 .sp
  46 .BI "char *strerror_r(int " errnum ", char *" buf ", size_t " buflen );
  47                         /* GNU-specific strerror_r() */
  48 .sp
  49 .B #define _XOPEN_SOURCE 600
  50 .B #include <string.h>
  51 .sp
  52 .BI "int strerror_r(int " errnum ", char *" buf ", size_t " buflen );
  53                         /* XSI-compliant strerror_r() */
  54 .fi
  55 .SH DESCRIPTION
  56 The \fBstrerror\fP() function returns a string describing the error
  57 code passed in the argument \fIerrnum\fP, possibly using the LC_MESSAGES
  58 part of the current locale to select the appropriate language.
  59 This string must not be modified by the application, but may be
  60 modified by a subsequent call to \fBperror\fP() or \fBstrerror\fP().
  61 No library function will modify this string.
  62
  63 The \fBstrerror_r\fP() function is similar to \fBstrerror\fP(), but is
  64 thread safe.
  65 This function is available in two versions:
  66 an XSI-compliant version specified in POSIX.1-2001,
  67 and a GNU-specific version (available since glibc 2.0).
  68 If _XOPEN_SOURCE is defined with the value 600,
  69 then the XSI-compliant version is provided,
  70 otherwise the GNU-specific version is provided.
  71
  72 The XSI-compliant
  73 .BR strerror_r ()
  74 is preferred for portable applications.
  75 It returns the error string in the user-supplied buffer
  76 .I buf
  77 of length
  78 .IR buflen .
  79
  80 The GNU-specific
  81 .BR strerror_r ()
  82 returns a pointer to a string containing the error message.
  83 This may be either a pointer to a string that the function stores in
  84 .IR buf ,
  85 or a pointer to some (immutable) static string
  86 (in which case
  87 .I buf
  88 is unused).
  89 If the function stores a string in
  90 .IR buf ,
  91 then at most
  92 .I buflen
  93 bytes are stored (the string may be truncated if
  94 .I buflen
  95 is too small) and the string always includes a terminating null byte.
  96 .SH "RETURN VALUE"
  97 The \fBstrerror\fP() and \fBstrerror_r\fP() functions return
  98 the appropriate error description string,
  99 or an "Unknown error nnn" message if the error number is unknown.
 100
 101 The XSI-compliant \fBstrerror_r\fP() function returns 0 on success;
 102 on error, \-1 is returned and
 103 .I errno
 104 is set to indicate the error.
 105 .SH ERRORS
 106 .TP
 107 .B EINVAL
 108 The value of
 109 .I errnum
 110 is not a valid error number.
 111 .TP
 112 .B ERANGE
 113 Insufficient storage was supplied to contain the error description string.
 114 .SH "CONFORMING TO"
 115 \fBstrerror\fP() is specified by POSIX.1-2001, C89, C99.
 116 \fBstrerror_r\fP() is specified by POSIX.1-2001.
 117
 118 The GNU-specific
 119 .BR strerror_r ()
 120 function is a non-standard extension.
 121
 122 POSIX.1-2001 permits
 123 .BR strerror ()
 124 to set
 125 .I errno
 126 if the call encounters an error, but does not specify what
 127 value should be returned as the function result in the event of an error.
 128 On some systems,
 129 .\" e.g., Solaris 8, HP-UX 11
 130 .BR strerror ()
 131 returns NULL if the error number is unknown.
 132 On other systems,
 133 .\" e.g., FreeBSD 5.4, Tru64 5.1B
 134 .BR strerror ()
 135 returns a string something like "Error nnn occurred" and sets
 136 .I errno
 137 to
 138 .B EINVAL
 139 if the error number is unknown.
 140 .SH "SEE ALSO"
 141 .BR err (3),
 142 .BR errno (3),
 143 .BR error (3),
 144 .BR perror (3),
 145 .BR strsignal (3),
 146 .BR feature_test_macros (7)