1.\" $NetBSD: strerror.3,v 1.24 2020/04/04 21:29:54 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 April 4, 2020 36.Dt STRERROR 3 37.Os 38.Sh NAME 39.Nm perror , 40.Nm strerror , 41.Nm strerror_l , 42.\" .Nm strerror_lr , 43.Nm strerror_r , 44.Nm sys_errlist , 45.Nm sys_nerr 46.Nd system error messages 47.Sh LIBRARY 48.Lb libc 49.Sh SYNOPSIS 50.In stdio.h 51.Ft void 52.Fn perror "const char *string" 53.In errno.h 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.Ft int 60.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen" 61.Ft "char *" 62.Fn strerror_l "int errnum" "locale_t loc" 63.\".Ft int 64.\".Fn strerror_lr "int errnum" "char *strerrbuf" "size_t buflen" "locale_t loc" 65.Sh DESCRIPTION 66The 67.Fn strerror , 68.Fn strerror_l , 69.\".Fn strerror_lr , 70.Fn strerror_r , 71and 72.Fn perror 73functions look up the language-dependent error message 74string corresponding to an error number. 75.Pp 76The 77.Fn strerror 78function accepts an error number argument 79.Fa errnum 80and returns a pointer to the corresponding 81message string. 82The application should not attempt to modify the 83returned string, it may be shared, or read only. 84.Pp 85The 86.Fn strerror_r 87function renders the same result into 88.Fa strerrbuf 89for a maximum of 90.Fa buflen 91characters (including terminator) and returns 0 upon success. 92.Pp 93The 94.Fn strerror_l 95function is like 96.Fn strerror 97but provides in 98.Fa loc 99the locale to be used to obtain the language for the message, 100rather than using the application's current locale. 101.\".Pp 102.\"The 103.\".Fn strerror_lr 104.\"function is to 105.\".Fn strerror_l 106.\"as 107.\".Fn strerror_r 108.\"is to 109.\".Fn strerror . 110.Pp 111The 112.Fn perror 113function finds the error message corresponding to the current 114value of the global variable 115.Va errno 116.Pq Xr intro 2 117and writes it, followed by a newline, to the 118standard error file descriptor. 119If the argument 120.Fa string 121is 122.Pf non- Dv NULL 123and does not point to the nul character, 124this string is prepended to the message 125string and separated from it by 126a colon and space 127.Pq Dq Li ":\ " ; 128otherwise, only the error message string is printed. 129Note that in most cases the 130.Xr err 3 131and 132.Xr warn 3 133family of functions is preferable to 134.Fn perror ; 135they are more flexible and also print the program name. 136.Pp 137If the error number is not recognized, these functions return an error message 138string containing 139.\" , in the appropriate language, 140.Dq Li "Unknown error:\ " 141followed by the error number in decimal. 142To warn about this, 143.Fn strerror 144and 145.Fn strerror_l 146set 147.Dv errno 148to 149.Er EINVAL , 150and 151.Fn strerror_r 152.\"and 153.\".Fn strerror_lr 154returns 155.Er EINVAL . 156In other cases, except where noted below, 157.Dv errno 158is not altered, so applications should set it to a known value 159(usually zero) before calling either 160.Fn strerror 161or 162.Fn strerror_l 163if the resulting value in 164.Dv errno 165is to be tested for this condition. 166Error numbers recognized by this implementation fall in 167the range 0 < 168.Fa errnum 169< 170.Fa sys_nerr . 171.Pp 172If insufficient storage is provided in 173.Fa strerrbuf 174(as specified in 175.Fa buflen ) 176to contain the error string, 177.Fn strerror_r 178.\" and 179.\" .Fn strerror_lr 180returns 181.Er ERANGE 182and 183.Fa strerrbuf 184will contain an error message that has been truncated and 185.Dv NUL 186terminated to fit the length specified by 187.Fa buflen . 188In extraordinary cases, it is possible that the internal 189buffer used by 190.Fn strerror 191and 192.Fn strerror_l 193may be too small for a translated message, 194in which case it will be truncated as indicated for 195.Fn strerror_r 196and 197.Dv errno 198will be set to 199.Er ERANGE . 200.Pp 201The POSIX locale message strings can be accessed directly using the external 202array 203.Va sys_errlist . 204The external value 205.Va sys_nerr 206contains a count of the messages in 207.Va sys_errlist . 208The use of these variables is deprecated; 209one of the 210.Fn strerror 211family of functions should be used instead. 212.Sh COMPATIBILITY 213Programs that attempt to use the deprecated 214.Va sys_errlist 215variable often fail to compile because they provide their own, 216inconsistent, declaration of it. 217Such programs should be updated to use 218.Fn strerror . 219.Sh ERRORS 220These functions may fail if: 221.Bl -tag -width Er 222.It Bq Er EINVAL 223The error number was out of range. 224.It Bq Er ERANGE 225The string buffer supplied was not large enough to hold the complete 226error message. 227.El 228.Sh SEE ALSO 229.Xr intro 2 , 230.Xr err 3 , 231.Xr psignal 3 , 232.Xr warn 3 233.Sh STANDARDS 234The 235.Fn perror 236and 237.Fn strerror 238functions conform to 239.St -isoC-99 . 240The 241.Fn strerror_r 242function conforms to 243.St -p1003.1-2001 . 244The 245.Fn strerror_l 246function conforms to 247.St -p1003.1-2008 . 248.Sh HISTORY 249The 250.Fn perror 251function first appeared in 252.At v4 . 253The 254.Fn strerror 255function first appeared in 256.Bx 4.3 Reno . 257The 258.Fn strerror_r 259function first appeared in 260.Nx 4.0 . 261The 262.Fn strerror_l 263function was first released in 264.Nx 7.0 . 265.\"The 266.\".Fn strerror_lr 267.\"function first appeared in 268.\".Nx 10.0 . 269.Sh BUGS 270The 271.Fn strerror 272function may return its result in a static buffer which 273will be overwritten by subsequent calls. 274For portable use, this must be assumed to be a subsequent 275call from the current, or any other, thread in the process. 276This implementation limits the issue to calls from the 277current thread. 278The 279.Fn strerror_l 280function has a similar restriction, but even in other 281implementations, is required to use thread local storage, 282so only other calls from the calling thread can overwrite 283the result. 284Both 285.Fn strerror 286and 287.Fn strerror_l 288use the same thread local storage; a call to either will destroy 289the result from an earlier call by the same thread of either of them. 290