1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 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 $ 34.\" $DragonFly: src/lib/libc/string/strerror.3,v 1.2 2003/06/17 04:26:46 dillon Exp $ 35.\" 36.Dd October 12, 2004 37.Dt STRERROR 3 38.Os 39.Sh NAME 40.Nm perror , 41.Nm strerror , 42.Nm strerror_r , 43.Nm sys_errlist , 44.Nm sys_nerr 45.Nd system error messages 46.Sh LIBRARY 47.Lb libc 48.Sh SYNOPSIS 49.In stdio.h 50.Ft void 51.Fn perror "const char *string" 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 error message string corresponding to an 66error 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 null 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 return an error message 103string containing 104.Dq Li "Unknown error:\ " 105followed by the error number in decimal. 106The 107.Fn strerror 108and 109.Fn strerror_r 110functions return 111.Er EINVAL 112as a warning. 113Error numbers recognized by this implementation fall in 114the range 0 < 115.Fa errnum 116< 117.Fa sys_nerr . 118.Pp 119If insufficient storage is provided in 120.Fa strerrbuf 121(as specified in 122.Fa buflen ) 123to contain the error string, 124.Fn strerror_r 125returns 126.Er ERANGE 127and 128.Fa strerrbuf 129will contain an error message that has been truncated and 130.Dv NUL 131terminated to fit the length specified by 132.Fa buflen . 133.Pp 134The message strings can be accessed directly using the external 135array 136.Va sys_errlist . 137The external value 138.Va sys_nerr 139contains a count of the messages in 140.Va sys_errlist . 141The use of these variables is deprecated; 142.Fn strerror 143or 144.Fn strerror_r 145should be used instead. 146.Sh SEE ALSO 147.Xr intro 2 , 148.Xr psignal 3 149.Sh STANDARDS 150The 151.Fn perror 152and 153.Fn strerror 154functions conform to 155.St -isoC-99 . 156The 157.Fn strerror_r 158function conforms to 159.St -p1003.1-2001 . 160.Sh HISTORY 161The 162.Fn strerror 163and 164.Fn perror 165functions first appeared in 166.Bx 4.4 . 167The 168.Fn strerror_r 169function was implemented in 170.Fx 4.4 171by 172.An Wes Peters Aq wes@FreeBSD.org . 173.Sh BUGS 174For unknown error numbers, the 175.Fn strerror 176function will return its result in a static buffer which 177may be overwritten by subsequent calls. 178.Pp 179The return type for 180.Fn strerror 181is missing a type-qualifier; it should actually be 182.Vt const char * . 183.Pp 184Programs that use the deprecated 185.Va sys_errlist 186variable often fail to compile because they declare it 187inconsistently. 188