NAME
err, verr,
errx, verrx,
errc, verrc,
warn, vwarn,
warnx, vwarnx,
warnc, vwarnc —
formatted error messages
LIBRARY
library “libc”
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
Theerr()
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
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:
err(1, "%s", string);