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.\" %sccs.include.redist.man% 9.\" 10.\" @(#)strerror.3 8.1 (Berkeley) 06/09/93 11.\" 12.Dd 13.Dt STRERROR 3 14.Os BSD 4 15.Sh NAME 16.Nm perror , 17.Nm strerror , 18.Nm sys_errlist , 19.Nm sys_nerr 20.Nd system error messages 21.Sh SYNOPSIS 22.Fd #include <stdio.h> 23.Ft void 24.Fn perror "const char *string" 25.Vt extern char *sys_errlist[]; 26.Vt extern int sys_nerr; 27.Fd #include <string.h> 28.Ft char * 29.Fn strerror "int errnum" 30.Sh DESCRIPTION 31The 32.Fn strerror 33and 34.Fn perror 35functions look up the error message string corresponding to an 36error number. 37.Pp 38The 39.Fn strerror 40function accepts an error number argument 41.Fa errnum 42and 43returns a pointer to the corresponding 44message string. 45.Pp 46The 47.Fn perror 48function finds the error message corresponding to the current 49value of the global variable 50.Va errno 51.Pq Xr intro 2 52and writes it, followed by a newline, to the 53standard error file descriptor. 54If the argument 55.Fa string 56is 57.Pf non- Dv NULL , 58it is prepended to the message 59string and separated from it by 60a colon and space 61.Pq Ql \&:\ \& . 62If 63.Fa string 64is 65.Dv NULL , 66only the error message string is printed. 67.Pp 68If 69.Fa errnum 70is not a recognized error number, 71the error message string will contain 72.Dq Li "Unknown error:\0 73followed by the error number in decimal. 74.Pp 75The message strings can be accessed directly using the external 76array 77.Fa sys_errlist . 78The external value 79.Fa sys_nerr 80contains a count of the messages in 81.Fa sys_errlist . 82The use of these variables is deprecated; 83.Fn strerror 84should be used instead. 85.Sh SEE ALSO 86.Xr intro 2 , 87.Xr psignal 3 88.Sh HISTORY 89The 90.Fn strerror 91and 92.Fn perror 93functions first appeared in 4.4BSD. 94.Sh BUGS 95For unknown error numbers, the 96.Fn strerror 97function will return its result in a static buffer which 98may be overwritten by subsequent calls. 99