1.\" $NetBSD: strerror.3,v 1.18 2015/05/09 19:01:53 dholland 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 9, 2015 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. 101Note that in most cases the 102.Xr err 3 103and 104.Xr warn 3 105family of functions is preferable to 106.Fn perror ; 107they are more flexible and also print the program name. 108.Pp 109If the error number is not recognized, these functions pass an error message 110string containing 111.Dq Li "Unknown error:\ " 112followed by the error number in decimal. 113To warn about this, 114.Fn strerror 115sets 116.Dv errno 117to 118.Er EINVAL , 119and 120.Fn strerror_r 121returns 122.Er EINVAL . 123Error numbers recognized by this implementation fall in 124the range 0 \*[Lt] 125.Fa errnum 126\*[Lt] 127.Fa sys_nerr . 128.Pp 129If insufficient storage is provided in 130.Fa strerrbuf 131(as specified in 132.Fa buflen ) 133to contain the error string, 134.Fn strerror_r 135returns 136.Er ERANGE 137and 138.Fa strerrbuf 139will contain an error message that has been truncated and 140.Dv NUL 141terminated to fit the length specified by 142.Fa buflen . 143.Pp 144The message strings can be accessed directly using the external 145array 146.Va sys_errlist . 147The external value 148.Va sys_nerr 149contains a count of the messages in 150.Va sys_errlist . 151The use of these variables is deprecated; 152.Fn strerror 153or 154.Fn strerror_r 155should be used instead. 156.Sh SEE ALSO 157.Xr intro 2 , 158.Xr err 3 , 159.Xr psignal 3 , 160.Xr warn 3 161.Sh STANDARDS 162The 163.Fn perror 164and 165.Fn strerror 166functions conform to 167.St -isoC-99 . 168The 169.Fn strerror_r 170function conforms to 171.St -p1003.1-2001 . 172.Sh HISTORY 173The 174.Fn perror 175function first appeared in 176.At v4 . 177The 178.Fn strerror 179function first appeared in 180.Bx 4.3 Reno . 181The 182.Fn strerror_r 183function first appeared in 184.Nx 4.0 . 185.Sh BUGS 186For unknown error numbers, the 187.Fn strerror 188function will return its result in a static buffer which 189may be overwritten by subsequent calls. 190.Pp 191The return type for 192.Fn strerror 193is missing a type-qualifier; it should actually be 194.Vt const char * . 195.Pp 196Programs that use the deprecated 197.Va sys_errlist 198variable often fail to compile because they declare it 199inconsistently. 200