$OpenBSD: err.3,v 1.20 2014/04/23 16:26:33 jmc Exp $ 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 ...
NAMEerrc verrc warnc vwarnc - formatted error messages
SYNOPSISIn err.h (See libbsd(7) for include usage.) Ft void Fn errc int status int code const char *fmt ... Ft void Fn verrc int status int code const char *fmt va_list args Ft void Fn warnc int code const char *fmt ... Ft void Fn vwarnc int code const char *fmt va_list args
DESCRIPTIONThe 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, followed by a colon (`:' ) character and a space, are output. The text that follows depends on the function being called. The Fa fmt specification (and associated arguments) may be any format allowed by printf(3) or NULL If the Fa fmt argument is not NULL the formatted error message is output.
The functions all output an error message string affiliated with an error value (see strerror(3)), preceded by a colon character and a space if Fa fmt is not NULL That is, the output is as follows:
progname: fmt: error message string
if Fa fmt is not NULL or:
progname: error message string
if it is.
The argument Fa code is used as the error value instead of the current value of the global variable errno
In all cases, the output is followed by a newline character.
The Fn errc , and Fn verrc functions do not return, but exit with the value of the argument Fa status .
EXAMPLESDisplay the current errno information string and exit:
if ((p = malloc(size)) == NULL) err(1, NULL); if ((fd = open(file_name, O_RDONLY, 0)) == -1) err(1, "%s", file_name);
Display an error message and exit:
if (tm.tm_hour < START_TIME) errx(1, "too early, wait until %s", start_time_string);
Warn of an error:
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) err(1, "%s", block_device);
SEE ALSOerr(3) exit(3), perror(3), printf(3), strerror(3)
HISTORYThe functions Fn errc , Fn verrc , Fn warnc , and Fn vwarnc first appeared in Fx 3.0 , Nx 7.0 and Ox 5.6 .
CAVEATSIt is important never to pass a string with user-supplied data as a format without using `%s' An attacker can put format specifiers in the string to mangle the stack, leading to a possible security hole. This holds true even if the string has been built ``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 family of functions.
Always be sure to use the proper secure idiom:
errc(1, 0, "%s", string);