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.\" $FreeBSD$ 38.\" 39.Dd June 9, 1993 40.Dt STRERROR 3 41.Os BSD 4 42.Sh NAME 43.Nm perror , 44.Nm strerror , 45.Nm sys_errlist , 46.Nm sys_nerr 47.Nd system error messages 48.Sh SYNOPSIS 49.Fd #include <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.Fd #include <string.h> 55.Ft char * 56.Fn strerror "int errnum" 57.Sh DESCRIPTION 58The 59.Fn strerror 60and 61.Fn perror 62functions look up the error message string corresponding to an 63error number. 64.Pp 65The 66.Fn strerror 67function accepts an error number argument 68.Fa errnum 69and 70returns a pointer to the corresponding 71message string. 72.Pp 73The 74.Fn perror 75function finds the error message corresponding to the current 76value of the global variable 77.Va errno 78.Pq Xr intro 2 79and writes it, followed by a newline, to the 80standard error file descriptor. 81If the argument 82.Fa string 83is 84.Pf non- Dv NULL 85and does not point to the null character, 86this string is prepended to the message 87string and separated from it by 88a colon and space 89.Pq Ql \&:\ \& ; 90otherwise, only the error message string is printed. 91.Pp 92If 93.Fa errnum 94is not a recognized error number, 95the error message string will contain 96.Dq Li "Unknown error:\0 97followed by the error number in decimal. 98.Pp 99The message strings can be accessed directly using the external 100array 101.Va sys_errlist . 102The external value 103.Va sys_nerr 104contains a count of the messages in 105.Va sys_errlist . 106The use of these variables is deprecated; 107.Fn strerror 108should be used instead. 109.Sh SEE ALSO 110.Xr intro 2 , 111.Xr psignal 3 112.Sh HISTORY 113The 114.Fn strerror 115and 116.Fn perror 117functions first appeared in 118.Bx 4.4 . 119.Sh BUGS 120For unknown error numbers, the 121.Fn strerror 122function will return its result in a static buffer which 123may be overwritten by subsequent calls. 124.Pp 125Programs that use the deprecated 126.Va sys_errlist 127variable often fail to compile because they declare it 128inconsistently. 129