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.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)strerror.3 8.1 (Berkeley) 6/9/93 33.\" $FreeBSD$ 34.\" 35.Dd April 5, 2011 36.Dt STRERROR 3 37.Os 38.Sh NAME 39.Nm perror , 40.Nm strerror , 41.Nm strerror_r , 42.Nm sys_errlist , 43.Nm sys_nerr 44.Nd system error messages 45.Sh LIBRARY 46.Lb libc 47.Sh SYNOPSIS 48.In stdio.h 49.Ft void 50.Fn perror "const char *string" 51.Vt extern const char * const sys_errlist[] ; 52.Vt extern const int sys_nerr ; 53.In string.h 54.Ft "char *" 55.Fn strerror "int errnum" 56.Ft int 57.Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen" 58.Sh DESCRIPTION 59The 60.Fn strerror , 61.Fn strerror_r 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 returns a pointer to the corresponding 72message string. 73.Pp 74The 75.Fn strerror_r 76function renders the same result into 77.Fa strerrbuf 78for a maximum of 79.Fa buflen 80characters and returns 0 upon success. 81.Pp 82The 83.Fn perror 84function finds the error message corresponding to the current 85value of the global variable 86.Va errno 87.Pq Xr intro 2 88and writes it, followed by a newline, to the 89standard error file descriptor. 90If the argument 91.Fa string 92is 93.Pf non- Dv NULL 94and does not point to the null character, 95this string is prepended to the message 96string and separated from it by 97a colon and space 98.Pq Dq Li ":\ " ; 99otherwise, only the error message string is printed. 100.Pp 101If the error number is not recognized, these functions return an error message 102string containing 103.Dq Li "Unknown error:\ " 104followed by the error number in decimal. 105The 106.Fn strerror 107and 108.Fn strerror_r 109functions return 110.Er EINVAL 111as a warning. 112Error numbers recognized by this implementation fall in 113the range 0 < 114.Fa errnum 115< 116.Fa sys_nerr . 117The number 0 is also recognized, although applications that take advantage of 118this are likely to use unspecified values of 119.Va errno . 120.Pp 121If insufficient storage is provided in 122.Fa strerrbuf 123(as specified in 124.Fa buflen ) 125to contain the error string, 126.Fn strerror_r 127returns 128.Er ERANGE 129and 130.Fa strerrbuf 131will contain an error message that has been truncated and 132.Dv NUL 133terminated to fit the length specified by 134.Fa buflen . 135.Pp 136The message strings can be accessed directly using the external 137array 138.Va sys_errlist . 139The external value 140.Va sys_nerr 141contains a count of the messages in 142.Va sys_errlist . 143The use of these variables is deprecated; 144.Fn strerror 145or 146.Fn strerror_r 147should be used instead. 148.Sh SEE ALSO 149.Xr intro 2 , 150.Xr err 3 , 151.Xr psignal 3 152.Sh STANDARDS 153The 154.Fn perror 155and 156.Fn strerror 157functions conform to 158.St -isoC-99 . 159The 160.Fn strerror_r 161function conforms to 162.St -p1003.1-2001 . 163.Sh HISTORY 164The 165.Fn strerror 166and 167.Fn perror 168functions first appeared in 169.Bx 4.4 . 170The 171.Fn strerror_r 172function was implemented in 173.Fx 4.4 174by 175.An Wes Peters Aq wes@FreeBSD.org . 176.Sh BUGS 177For unknown error numbers, the 178.Fn strerror 179function will return its result in a static buffer which 180may be overwritten by subsequent calls. 181.Pp 182The return type for 183.Fn strerror 184is missing a type-qualifier; it should actually be 185.Vt const char * . 186.Pp 187Programs that use the deprecated 188.Va sys_errlist 189variable often fail to compile because they declare it 190inconsistently. 191