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 LIBRARY 49.Lb libc 50.Sh SYNOPSIS 51.Fd #include <stdio.h> 52.Ft void 53.Fn perror "const char *string" 54.Vt extern const char * const sys_errlist[]; 55.Vt extern const int sys_nerr; 56.Fd #include <string.h> 57.Ft char * 58.Fn strerror "int errnum" 59.Sh DESCRIPTION 60The 61.Fn strerror 62and 63.Fn perror 64functions look up the error message string corresponding to an 65error number. 66.Pp 67The 68.Fn strerror 69function accepts an error number argument 70.Fa errnum 71and 72returns a pointer to the corresponding 73message string. 74.Pp 75The 76.Fn perror 77function finds the error message corresponding to the current 78value of the global variable 79.Va errno 80.Pq Xr intro 2 81and writes it, followed by a newline, to the 82standard error file descriptor. 83If the argument 84.Fa string 85is 86.Pf non- Dv NULL 87and does not point to the null character, 88this string is prepended to the message 89string and separated from it by 90a colon and space 91.Pq Ql \&:\ \& ; 92otherwise, only 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.Va sys_errlist . 104The external value 105.Va sys_nerr 106contains a count of the messages in 107.Va 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 120.Bx 4.4 . 121.Sh BUGS 122For unknown error numbers, the 123.Fn strerror 124function will return its result in a static buffer which 125may be overwritten by subsequent calls. 126.Pp 127Programs that use the deprecated 128.Va sys_errlist 129variable often fail to compile because they declare it 130inconsistently. 131