ERR(3) BSD Programmer's Manual ERR(3)NAME
err, verr, errx, verrx, warn, vwarn, warnx, vwarnx - formatted error mes-
sages
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
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.
EXAMPLES
Display the current errno information string and exit:
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);
SEE ALSOexit(3), perror(3), printf(3), strerror(3)HISTORY
The err() and warn() functions first appeared in 4.4BSD.
CAVEATS
It is important never to pass a string with user-supplied data as a for-
mat 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(), 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);
MirOS BSD #10-current August 8, 1997 1