ERR(3) |
NetBSD Library Functions Manual |
ERR(3) |
NAME
err, verr, errx, verrx, warn, vwarn, warnx, vwarnx — formatted error messages
LIBRARY
Standard C Library (libc, -lc)
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
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 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
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);
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 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);