ERR(3) | Library Functions Manual | ERR(3) |
err
, verr
,
errx
, verrx
,
warn
, vwarn
,
warnx
, vwarnx
—
#include <err.h>
void
err
(int
eval, const char
*fmt, ...);
void
verr
(int
eval, 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
warnx
(const
char *fmt,
...);
void
vwarnx
(const
char *fmt, va_list
args);
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), a simple string, or
NULL
. If the fmt argument is not
NULL
, the formatted error message is output.
In the case of the err
(),
verr
(), warn
(), and
vwarn
() functions only, the error message string
affiliated with the current value of the global variable
errno is output (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 counterpart functions, errx
(),
verrx
(), warnx
(), and
vwarnx
(), do not output the error message string, so
the output looks like the following:
progname: fmt
In all cases, the output is followed by a newline character.
The err
(), verr
(),
errx
(), and verrx
()
functions do not return, but exit with the value of the argument
eval.
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);
err
() and warn
() functions
first appeared in 4.4BSD.
%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:
err(1, "%s", string);
May 31, 2007 | OpenBSD-5.1 |