NAME
err,
verr,
errx,
verrx,
errc,
verrc,
warn,
vwarn,
warnx,
vwarnx,
warnc,
vwarnc
—
formatted error messages
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <err.h>
void
err(
int
status,
const char
*fmt,
...);
void
verr(
int
status,
const char
*fmt,
va_list args);
void
errx(
int
status,
const char
*fmt,
...);
void
verrx(
int
status,
const char
*fmt,
va_list args);
void
errc(
int
status,
int code,
const char *fmt,
...);
void
verrc(
int
status,
int code,
const char *fmt,
va_list args);
void
warn(
const char
*fmt,
...);
void
vwarn(
const char
*fmt,
va_list args);
void
warnx(
const char
*fmt,
...);
void
vwarnx(
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 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
fmt argument is not
NULL
, the formatted error message is output. In the
case of the
err(),
verr(),
warn(), and
vwarn() functions, the error
message string affiliated with the current value of the global variable
errno is output next, preceded by a colon character and
a space if
fmt is not
NULL
. In
all cases, the output is followed by a newline character. The
errc(),
verrc(),
warnc(), and
vwarnc() functions take an
additional
code argument to be used as the error number
instead of using the global
errno variable. The
errx(),
verrx(),
warnx(), and
vwarnx() functions will not
output this error message string.
The
err(),
verr(),
errx(),
and
verrx() functions do not return, but instead cause the
program to terminate with the status value given by the argument
status. It is often appropriate to use the value
EXIT_FAILURE
, defined in
<stdlib.h>, as the
status argument given to these functions.
EXAMPLES
Display the current
errno information string and terminate
with status indicating failure:
if ((p = malloc(size)) == NULL)
err(EXIT_FAILURE, NULL);
if ((fd = open(file_name, O_RDONLY, 0)) == -1)
err(EXIT_FAILURE, "%s", file_name);
Display an error message and terminate with status indicating failure:
if (tm.tm_hour < START_TIME)
errx(EXIT_FAILURE, "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)
warn("%s", block_device);
SEE ALSO
exit(3),
getprogname(3),
strerror(3)
HISTORY
The
err() and
warn() functions first
appeared in
4.4BSD. The
errc() and
warnc() functions first appeared in
FreeBSD
3.0 and
NetBSD 7.0.
CAVEATS
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 your stack, leading to a possible
security hole. This holds true even if you have built the string “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: