| ERR(3C) | Standard C Library Functions | ERR(3C) |
err, errc,
errx, warn,
warnc, warnx,
verr, verrc,
verrx, vwarn,
vwarnc, vwarnx —
formatted error messages
#include
<err.h>
void
err(int eval,
const char *fmt, ...);
void
errc(int eval,
int code, const char *fmt,
...);
void
errx(int eval,
const char *fmt, ...);
void
warn(const char *fmt,
...);
void
warnc(int code,
const char *fmt, ...);
void
warnx(const char *fmt,
...);
void
verr(int eval,
const char *fmt, va_list
args);
void
verrc(int eval,
int code, const char *fmt,
va_list args);
void
verrx(int eval,
const char *fmt, va_list
args);
void
vwarn(const char *fmt,
va_list args);
void
vwarnc(int code,
const char *fmt, va_list
args);
void
vwarnx(const char *fmt,
va_list args);
The
err()
and
warn()
family of functions display a formatted error message to standard error. In
all cases, the last component of the program name, followed by 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(),
errc(),
warn(),
warnc(),
verr(), verrc(),
vwarn()
and
vwarnc()
functions, an error message obtained from
strerror(3C) is output next,
preceded by a colon character and a space if fmt is
not NULL. The err(),
warn(), verr() and
vwarn() functions produce the error string
affiliated with the current value of the global variable
errno. The errc(),
warnc(), verrc() and
vwarnc() functions use the provided
code value to look up the error message.
The
errx(),
verrx(),
warnx()
and
vwarnx()
functions will not output this error message string.
In all cases, the output is followed by a newline character.
The
err(),
errc(),
errx(),
verr(),
verrc()
and verrx() functions do not return, but instead
cause the program to terminate with the status value given by the
eval argument.
Example 1 Display the current errno information string and terminate with status indicating failure.
#include <err.h> ... if ((p = malloc(size)) == NULL) err(EXIT_FAILURE, NULL); if ((fd = open(file_name, O_RDONLY, 0)) == -1) err(EXIT_FAILURE, "%s", file_name);
Example 2 Display an error message and terminate with status indicating failure.
if (tm.tm_hour < START_TIME) errx(EXIT_FAILURE, "wait until %s", start_time_string);
Example 3 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);
Example 4 Warn of an error using a custom error code
int error = function_returning_error_code(); if (error != 0) warnc(error, "%s", "function did not succeed");
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(3C), as the
resulting string can 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);
These functions are safe to use in multithreaded applications as long as setlocale(3C) is not being called to change the locale.
exit(3C), getexecname(3C), setlocale(3C), strerror(3C), attributes(7)
The functions described in this man page are BSD extensions and should not be used in portable code.
| November 15, 2022 | OmniOS |