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.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" @(#)strerror.3 8.1 (Berkeley) 6/9/93 37.\" 38.Dd June 9, 1993 39.Dt STRERROR 3 40.Os BSD 4 41.Sh NAME 42.Nm perror , 43.Nm strerror , 44.Nm sys_errlist , 45.Nm sys_nerr 46.Nd system error messages 47.Sh SYNOPSIS 48.Fd #include <stdio.h> 49.Ft void 50.Fn perror "const char *string" 51.Vt extern const char * const sys_errlist[]; 52.Vt extern const int sys_nerr; 53.Fd #include <string.h> 54.Ft char * 55.Fn strerror "int errnum" 56.Sh DESCRIPTION 57The 58.Fn strerror 59and 60.Fn perror 61functions look up the error message string corresponding to an 62error number. 63.Pp 64The 65.Fn strerror 66function accepts an error number argument 67.Fa errnum 68and 69returns a pointer to the corresponding 70message string. 71.Pp 72The 73.Fn perror 74function finds the error message corresponding to the current 75value of the global variable 76.Va errno 77.Pq Xr intro 2 78and writes it, followed by a newline, to the 79standard error file descriptor. 80If the argument 81.Fa string 82is 83.Pf non- Dv NULL 84and does not point to the null character, 85this string is prepended to the message 86string and separated from it by 87a colon and space 88.Pq Ql \&:\ \& ; 89otherwise, only the error message string is printed. 90.Pp 91If 92.Fa errnum 93is not a recognized error number, 94the error message string will contain 95.Dq Li "Unknown error:\0 96followed by the error number in decimal. 97.Pp 98The message strings can be accessed directly using the external 99array 100.Va sys_errlist . 101The external value 102.Va sys_nerr 103contains a count of the messages in 104.Va sys_errlist . 105The use of these variables is deprecated; 106.Fn strerror 107should be used instead. 108.Sh SEE ALSO 109.Xr intro 2 , 110.Xr psignal 3 111.Sh HISTORY 112The 113.Fn strerror 114and 115.Fn perror 116functions first appeared in 117.Bx 4.4 . 118.Sh BUGS 119For unknown error numbers, the 120.Fn strerror 121function will return its result in a static buffer which 122may be overwritten by subsequent calls. 123.Pp 124Programs that use the deprecated 125.Va sys_errlist 126variable often fail to compile because they declare it 127inconsistently. 128