1.\" $NetBSD: strerror.3,v 1.15 2006/10/16 08:48:45 wiz Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" the American National Standards Committee X3, on Information 8.\" Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)strerror.3 8.1 (Berkeley) 6/9/93 35.Dd May 22, 2006 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.In errno.h 52.Vt extern const char * const sys_errlist[] ; 53.Vt extern const int sys_nerr ; 54.In string.h 55.Ft "char *" 56.Fn strerror "int errnum" 57.Ft int 58.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen" 59.Sh DESCRIPTION 60The 61.Fn strerror , 62.Fn strerror_r , 63and 64.Fn perror 65functions look up the language-dependent error message 66string corresponding to an error number. 67.Pp 68The 69.Fn strerror 70function accepts an error number argument 71.Fa errnum 72and returns a pointer to the corresponding 73message string. 74.Pp 75The 76.Fn strerror_r 77function renders the same result into 78.Fa strerrbuf 79for a maximum of 80.Fa buflen 81characters and returns 0 upon success. 82.Pp 83The 84.Fn perror 85function finds the error message corresponding to the current 86value of the global variable 87.Va errno 88.Pq Xr intro 2 89and writes it, followed by a newline, to the 90standard error file descriptor. 91If the argument 92.Fa string 93is 94.Pf non- Dv NULL 95and does not point to the nul character, 96this string is prepended to the message 97string and separated from it by 98a colon and space 99.Pq Dq Li ":\ " ; 100otherwise, only the error message string is printed. 101.Pp 102If the error number is not recognized, these functions pass an error message 103string containing 104.Dq Li "Unknown error:\ " 105followed by the error number in decimal. 106To warn about this, 107.Fn strerror 108sets 109.Dv errno 110to 111.Er EINVAL , 112and 113.Fn strerror_r 114returns 115.Er EINVAL . 116Error numbers recognized by this implementation fall in 117the range 0 \*[Lt] 118.Fa errnum 119\*[Lt] 120.Fa sys_nerr . 121.Pp 122If insufficient storage is provided in 123.Fa strerrbuf 124(as specified in 125.Fa buflen ) 126to contain the error string, 127.Fn strerror_r 128returns 129.Er ERANGE 130and 131.Fa strerrbuf 132will contain an error message that has been truncated and 133.Dv NUL 134terminated to fit the length specified by 135.Fa buflen . 136.Pp 137The message strings can be accessed directly using the external 138array 139.Va sys_errlist . 140The external value 141.Va sys_nerr 142contains a count of the messages in 143.Va sys_errlist . 144The use of these variables is deprecated; 145.Fn strerror 146or 147.Fn strerror_r 148should be used instead. 149.Sh SEE ALSO 150.Xr intro 2 , 151.Xr psignal 3 152.Sh STANDARDS 153The 154.Fn perror 155and 156.Fn strerror 157functions conform to 158.St -isoC-99 . 159The 160.Fn strerror_r 161function conforms to 162.St -p1003.1-2001 . 163.Sh HISTORY 164The 165.Fn strerror 166and 167.Fn perror 168functions first appeared in 169.Bx 4.4 . 170The 171.Fn strerror_r 172function first appeared in 173.Nx 4.0 . 174.Sh BUGS 175For unknown error numbers, the 176.Fn strerror 177function will return its result in a static buffer which 178may be overwritten by subsequent calls. 179.Pp 180The return type for 181.Fn strerror 182is missing a type-qualifier; it should actually be 183.Vt const char * . 184.Pp 185Programs that use the deprecated 186.Va sys_errlist 187variable often fail to compile because they declare it 188inconsistently. 189