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 Nov 26, 2001 40.Dt STRERROR 3 41.Os 42.Sh NAME 43.Nm perror , 44.Nm strerror , 45.Nm strerror_r , 46.Nm sys_errlist , 47.Nm sys_nerr 48.Nd system error messages 49.Sh LIBRARY 50.Lb libc 51.Sh SYNOPSIS 52.In stdio.h 53.Ft void 54.Fn perror "const char *string" 55.Vt extern const char * const sys_errlist[] ; 56.Vt extern const int sys_nerr ; 57.In string.h 58.Ft char * 59.Fn strerror "int errnum" 60.Ft int 61.Fn strerror_r "int errnum" "char * strerrbuf" "size_t buflen" 62.Sh DESCRIPTION 63The 64.Fn strerror , 65.Fn strerror_r 66and 67.Fn perror 68functions look up the error message string corresponding to an 69error number. 70.Pp 71The 72.Fn strerror 73function accepts an error number argument 74.Fa errnum 75and returns a pointer to the corresponding 76message string. 77.Pp 78The 79.Fn strerror_r 80function renders the same result into 81.Fa strerrbuf 82for a maximum of 83.Fa buflen 84characters and returns 0 upon success. If insufficient 85storage is provided in 86.Fa strerrbuf 87(as specified in 88.Fa buflen ) 89to contain the error string, 90.Er ERANGE 91is returned and the string in 92.Fa strerrbuf 93may not be null-terminated. 94.Pp 95The 96.Fn perror 97function finds the error message corresponding to the current 98value of the global variable 99.Va errno 100.Pq Xr intro 2 101and writes it, followed by a newline, to the 102standard error file descriptor. 103If the argument 104.Fa string 105is 106.Pf non- Dv NULL 107and does not point to the null character, 108this string is prepended to the message 109string and separated from it by 110a colon and space 111.Pq Ql \&:\ \& ; 112otherwise, only the error message string is printed. 113.Pp 114If 115.Fa errnum 116is not a recognized error number, 117the error message string will contain 118.Dq Li "Unknown error:\ " 119followed by the error number in decimal. 120.Pp 121The message strings can be accessed directly using the external 122array 123.Va sys_errlist . 124The external value 125.Va sys_nerr 126contains a count of the messages in 127.Va sys_errlist . 128The use of these variables is deprecated; 129.Fn strerror 130or 131.Fn strerror_r 132should be used instead. 133.Sh SEE ALSO 134.Xr intro 2 , 135.Xr psignal 3 136.Sh HISTORY 137The 138.Fn strerror 139and 140.Fn perror 141functions first appeared in 142.Bx 4.4 . 143The 144.Fn strerror_r 145function was implemented in 146.Fx 4.4 147by 148.An Wes Peters 149.Aq wes@freebsd.org . 150.Sh BUGS 151For unknown error numbers, the 152.Fn strerror 153function will return its result in a static buffer which 154may be overwritten by subsequent calls. 155.Pp 156Programs that use the deprecated 157.Va sys_errlist 158variable often fail to compile because they declare it 159inconsistently. 160