ERR(3C)ERR(3C)NAME
err, verr, errx, verrx, warn, vwarn, warnx, vwarnx - formatted error
messages
SYNOPSIS
#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);
DESCRIPTION
The err() and warn() family of functions display a formatted error mes‐
sage on the standard error output. In all cases, the last component of
the program name, followed by a colon character and a space, are out‐
put. If the fmt argument is not NULL, the formatted error message is
output. In the case of the err(), verr(), warn(), and vwarn() func‐
tions, 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 errx(), verrx(), warnx(), and vwarnx() func‐
tions 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.
EXAMPLES
Example 1 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);
Example 2 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);
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);
WARNINGS
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 func‐
tion 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);
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬──────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼──────────────────────┤
│Interface Stability │ Committed │
├────────────────────┼──────────────────────┤
│MT-Level │ Safe with Exceptions │
└────────────────────┴──────────────────────┘
These functions are safe to use in multithreaded applications as long
as setlocale(3C) is not being called to change the locale.
SEE ALSOexit(3C), getexecname(3C), setlocale(3C), strerror(3C), attributes(5)
Aug 20, 2007 ERR(3C)
