err,
verr,
errc,
verrc,
errx,
verrx,
warn,
vwarn,
warnc,
vwarnc,
warnx,
vwarnx —
formatted error messages
#include
<err.h>
void
err(
int
eval,
const char
*fmt,
...);
void
verr(
int
eval,
const char
*fmt,
va_list
args);
void
errc(
int
eval,
int
code,
const char
*fmt,
...);
void
verrc(
int
eval,
int
code,
const char
*fmt,
va_list
args);
void
errx(
int
eval,
const char
*fmt,
...);
void
verrx(
int
eval,
const char
*fmt,
va_list
args);
void
warn(
const
char *fmt,
...);
void
vwarn(
const
char *fmt,
va_list args);
void
warnc(
int
code,
const char
*fmt,
...);
void
vwarnc(
int
code,
const char
*fmt,
va_list
args);
void
warnx(
const
char *fmt,
...);
void
vwarnx(
const
char *fmt,
va_list args);
The
err() and
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
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.
In the case of the
errx(),
verrx(),
warnx(), and
vwarnx() functions only, no additional text
is output, so the output looks like the following:
The other 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.
In the case of the
err(),
verr(),
warn(), and
vwarn() functions, the error value used is
the current value of the global variable
errno, while for the
errc(),
verrc(),
warnc(), and
vwarnc() function the argument
code is used.
In all cases, the output is followed by a newline character.
The
err(),
verr(),
errc(),
verrc(),
errx(), and
verrx() functions do not return, but exit
with the value of the argument
eval.
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);
exit(3),
perror(3),
printf(3),
strerror(3)
The functions
err(),
errx(),
verr(),
verrx(),
warn(),
warnx(),
vwarn(), and
vwarnx() first appeared in
4.4BSD. The functions
errc(),
verrc(),
warnc(), and
vwarnc() first appeared in
FreeBSD 3.0 and were ported to
OpenBSD 5.6.
It 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
snprintf(), as the resulting string may
still contain user-supplied conversion specifiers for later interpolation by
the
err() and
warn() functions.
Always be sure to use the proper secure idiom:
![[OpenBSD]](/openbsd.gif){kind=small}