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 November 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. 85.Pp 86The 87.Fn perror 88function finds the error message corresponding to the current 89value of the global variable 90.Va errno 91.Pq Xr intro 2 92and writes it, followed by a newline, to the 93standard error file descriptor. 94If the argument 95.Fa string 96is 97.Pf non- Dv NULL 98and does not point to the null character, 99this string is prepended to the message 100string and separated from it by 101a colon and space 102.Pq Dq Li ":\ " ; 103otherwise, only the error message string is printed. 104.Pp 105If 106.Fa errnum 107is not a recognized error number, 108.Fn strerror 109returns an error message string containing 110.Dq Li "Unknown error:\ " 111followed by the error number in decimal, while 112.Fn strerror_r 113leaves 114.Fa strerrbuf 115unchanged and returns 116.Er EINVAL . 117Error numbers recognized by this implementation fall in 118the range 0 \(<= 119.Fa errnum 120< 121.Fa sys_nerr . 122.Pp 123If insufficient storage is provided in 124.Fa strerrbuf 125(as specified in 126.Fa buflen ) 127to contain the error string, 128.Fn strerror_r 129returns 130.Er ERANGE 131and 132.Fa strerrbuf 133will contain an error message that has been truncated and 134.Dv NUL 135terminated to fit the length specified by 136.Fa buflen . 137.Pp 138The message strings can be accessed directly using the external 139array 140.Va sys_errlist . 141The external value 142.Va sys_nerr 143contains a count of the messages in 144.Va sys_errlist . 145The use of these variables is deprecated; 146.Fn strerror 147or 148.Fn strerror_r 149should be used instead. 150.Sh SEE ALSO 151.Xr intro 2 , 152.Xr psignal 3 153.Sh HISTORY 154The 155.Fn strerror 156and 157.Fn perror 158functions first appeared in 159.Bx 4.4 . 160The 161.Fn strerror_r 162function was implemented in 163.Fx 4.4 164by 165.An Wes Peters Aq wes@FreeBSD.org . 166.Sh BUGS 167For unknown error numbers, the 168.Fn strerror 169function will return its result in a static buffer which 170may be overwritten by subsequent calls. 171.Pp 172Programs that use the deprecated 173.Va sys_errlist 174variable often fail to compile because they declare it 175inconsistently. 176