Copyright (c) 1993
The Regents of the University of California. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
@(#)err.3 8.1 (Berkeley) 6/9/93
.Dd March 21, 2001 .Dt ERR 3 .Os .Sh NAME .Nm err , .Nm verr , .Nm errx , .Nm verrx , .Nm warn , .Nm vwarn , .Nm warnx , .Nm vwarnx .Nd formatted error messages .Sh LIBRARY .Lb libc .Sh SYNOPSIS n err.h .Ft void .Fn err "int status" "const char *fmt" "..." .Ft void .Fn verr "int status" "const char *fmt" "va_list args" .Ft void .Fn errx "int status" "const char *fmt" "..." .Ft void .Fn verrx "int status" "const char *fmt" "va_list args" .Ft void .Fn warn "const char *fmt" "..." .Ft void .Fn vwarn "const char *fmt" "va_list args" .Ft void .Fn warnx "const char *fmt" "..." .Ft void .Fn vwarnx "const char *fmt" "va_list args" .Sh DESCRIPTION The .Fn err and .Fn warn family of functions display a formatted error message on the standard error output. In all cases, the last component of the program name, a colon character, and a space are output. If the .Fa fmt argument is not .Dv NULL , the formatted error message is output. In the case of the .Fn err , .Fn verr , .Fn warn , and .Fn vwarn functions, the error message string affiliated with the current value of the global variable .Va errno is output next, preceded by a colon character and a space if .Fa fmt is not .Dv NULL . In all cases, the output is followed by a newline character. The .Fn errx , .Fn verrx , .Fn warnx , and .Fn vwarnx functions will not output this error message string.
p The .Fn err , .Fn verr , .Fn errx , and .Fn verrx functions do not return, but instead cause the program to terminate with the status value given by the argument .Fa status . It is often appropriate to use the value .Dv EXIT_FAILURE , defined in n stdlib.h , as the .Fa status argument given to these functions. .Sh EXAMPLES Display the current .Va errno information string and terminate with status indicating failure: d -literal -offset indent if ((p = malloc(size)) == NULL) err(EXIT_FAILURE, NULL); if ((fd = open(file_name, O_RDONLY, 0)) == -1) err(EXIT_FAILURE, "%s", file_name); .Ed
p Display an error message and terminate with status indicating failure: d -literal -offset indent if (tm.tm_hour \*[Lt] START_TIME) errx(EXIT_FAILURE, "too early, wait until %s", start_time_string); .Ed
p Warn of an error: d -literal -offset indent if ((fd = open(raw_device, O_RDONLY, 0)) == -1) warnx("%s: %s: trying the block device", raw_device, strerror(errno)); if ((fd = open(block_device, O_RDONLY, 0)) == -1) warn("%s", block_device); .Ed .Sh SEE ALSO .Xr exit 3 , .Xr getprogname 3 , .Xr strerror 3 .Sh HISTORY The .Fn err and .Fn warn functions first appeared in x 4.4 . .Sh CAVEATS It is important never to pass a string with user-supplied data as a format without using .Ql %s . An attacker can put format specifiers in the string to mangle your stack, leading to a possible security hole. This holds true even if you have built the string .Dq by hand using a function like .Fn snprintf , as the resulting string may still contain user-supplied conversion specifiers for later interpolation by the .Fn err and .Fn warn functions.
p Always be sure to use the proper secure idiom: d -literal -offset indent err(1, "%s", string); .Ed