1.\" $NetBSD: err.3,v 1.17 2003/04/16 13:34:36 wiz Exp $ 2.\" 3.\" Copyright (c) 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)err.3 8.1 (Berkeley) 6/9/93 35.\" 36.Dd March 21, 2001 37.Dt ERR 3 38.Os 39.Sh NAME 40.Nm err , 41.Nm verr , 42.Nm errx , 43.Nm verrx , 44.Nm warn , 45.Nm vwarn , 46.Nm warnx , 47.Nm vwarnx 48.Nd formatted error messages 49.Sh LIBRARY 50.Lb libc 51.Sh SYNOPSIS 52.In err.h 53.Ft void 54.Fn err "int status" "const char *fmt" "..." 55.Ft void 56.Fn verr "int status" "const char *fmt" "va_list args" 57.Ft void 58.Fn errx "int status" "const char *fmt" "..." 59.Ft void 60.Fn verrx "int status" "const char *fmt" "va_list args" 61.Ft void 62.Fn warn "const char *fmt" "..." 63.Ft void 64.Fn vwarn "const char *fmt" "va_list args" 65.Ft void 66.Fn warnx "const char *fmt" "..." 67.Ft void 68.Fn vwarnx "const char *fmt" "va_list args" 69.Sh DESCRIPTION 70The 71.Fn err 72and 73.Fn warn 74family of functions display a formatted error message on the standard 75error output. 76In all cases, the last component of the program name, a colon character, 77and a space are output. 78If the 79.Fa fmt 80argument is not 81.Dv NULL , 82the formatted error message is output. 83In the case of the 84.Fn err , 85.Fn verr , 86.Fn warn , 87and 88.Fn vwarn 89functions, the error message string affiliated with the current value of 90the global variable 91.Va errno 92is output next, preceded by a colon character and a space if 93.Fa fmt 94is not 95.Dv NULL . 96In all cases, the output is followed by a newline character. 97.Pp 98The 99.Fn err , 100.Fn verr , 101.Fn errx , 102and 103.Fn verrx 104functions do not return, but instead cause the program to terminate 105with the status value given by the argument 106.Fa status . 107It is often appropriate to use the value 108.Dv EXIT_FAILURE , 109defined in 110.Aq Ar stdlib.h , 111as the 112.Fa status 113argument given to these functions. 114.Sh EXAMPLES 115Display the current 116.Va errno 117information string and terminate with status indicating failure: 118.Bd -literal -offset indent 119if ((p = malloc(size)) == NULL) 120 err(EXIT_FAILURE, NULL); 121if ((fd = open(file_name, O_RDONLY, 0)) == -1) 122 err(EXIT_FAILURE, "%s", file_name); 123.Ed 124.Pp 125Display an error message and terminate with status indicating failure: 126.Bd -literal -offset indent 127if (tm.tm_hour \*[Lt] START_TIME) 128 errx(EXIT_FAILURE, "too early, wait until %s", 129 start_time_string); 130.Ed 131.Pp 132Warn of an error: 133.Bd -literal -offset indent 134if ((fd = open(raw_device, O_RDONLY, 0)) == -1) 135 warnx("%s: %s: trying the block device", 136 raw_device, strerror(errno)); 137if ((fd = open(block_device, O_RDONLY, 0)) == -1) 138 warn("%s", block_device); 139.Ed 140.Sh SEE ALSO 141.Xr exit 3 , 142.Xr getprogname 3 , 143.Xr strerror 3 144.Sh HISTORY 145The 146.Fn err 147and 148.Fn warn 149functions first appeared in 150.Bx 4.4 . 151.Sh CAVEATS 152It is important never to pass a string with user-supplied data as a 153format without using 154.Ql %s . 155An attacker can put format specifiers in the string to mangle your stack, 156leading to a possible security hole. 157This holds true even if you have built the string 158.Dq by hand 159using a function like 160.Fn snprintf , 161as the resulting string may still contain user-supplied conversion specifiers 162for later interpolation by the 163.Fn err 164and 165.Fn warn 166functions. 167.Pp 168Always be sure to use the proper secure idiom: 169.Bd -literal -offset indent 170err(1, "%s", string); 171.Ed 172