errc(3bsd) LOCAL errc(3bsd)
NAME
errc, verrc, warnc, vwarnc — formatted error messages
LIBRARY
Utility functions from BSD systems (libbsd, -lbsd)
SYNOPSIS
#include <err.h>
(See libbsd(7) for include usage.)
void
errc(int status, int code, const char *fmt, ...);
void
verrc(int status, int code, const char *fmt, va_list args);
void
warnc(int code, const char *fmt, ...);
void
vwarnc(int code, const char *fmt, va_list args);
DESCRIPTION
The err() and warn() family of functions display a formatted error mes-
sage 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
fmt specification (and associated arguments) may be any format allowed by
printf(3) or NULL. If the 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 fmt
is not NULL. That is, the output is as follows:
progname: fmt: error message string
if fmt is not NULL, or:
progname: error message string
if it is.
The argument 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 errc(), and verrc() functions do not return, but exit with the value
of the argument status.
EXAMPLES
Display 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 ALSO
err(3) exit(3), perror(3), printf(3), strerror(3)
HISTORY
The functions errc(), verrc(), warnc(), and vwarnc() first appeared in
FreeBSD 3.0, NetBSD 7.0 and OpenBSD 5.6.
CAVEATS
It is important never to pass a string with user-supplied data as a for-
mat 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 snprintf(), as the resulting string may still contain user-supplied
conversion specifiers for later interpolation by the err() and warn()
family of functions.
Always be sure to use the proper secure idiom:
errc(1, 0, "%s", string);
BSD April 23, 2014 BSD
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