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 char *sys_errlist[]; 52.Vt extern 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 , 84it is prepended to the message 85string and separated from it by 86a colon and space 87.Pq Ql \&:\ \& . 88If 89.Fa string 90is 91.Dv NULL , 92only the error message string is printed. 93.Pp 94If 95.Fa errnum 96is not a recognized error number, 97the error message string will contain 98.Dq Li "Unknown error:\0 99followed by the error number in decimal. 100.Pp 101The message strings can be accessed directly using the external 102array 103.Fa sys_errlist . 104The external value 105.Fa sys_nerr 106contains a count of the messages in 107.Fa sys_errlist . 108The use of these variables is deprecated; 109.Fn strerror 110should be used instead. 111.Sh SEE ALSO 112.Xr intro 2 , 113.Xr psignal 3 114.Sh HISTORY 115The 116.Fn strerror 117and 118.Fn perror 119functions first appeared in 4.4BSD. 120.Sh BUGS 121For unknown error numbers, the 122.Fn strerror 123function will return its result in a static buffer which 124may be overwritten by subsequent calls. 125