| ERR(3) | Library Functions Manual | ERR(3) | 
err, verr,
  errx, verrx,
  errc, verrc,
  warn, vwarn,
  warnx, vwarnx,
  warnc, vwarnc —
#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
  
  errc(int
    status, int code,
    const char *fmt,
    ...);
void
  
  verrc(int
    status, int code,
    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);
void
  
  warnc(int
    code, const char
    *fmt, ...);
void
  
  vwarnc(int
    code, 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, 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 errc(),
  verrc(), warnc(), and
  vwarnc() functions take an additional
  code argument to be used as the error number instead of
  using the global errno variable. The
  errx(), verrx(),
  warnx(), and vwarnx()
  functions will not output this error message string.
The err(), verr(),
    errc(), verrc(),
    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.
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);
err() and warn() functions
  first appeared in 4.4BSD. The
  errc() and warnc() functions
  first appeared in FreeBSD 3.0 and
  NetBSD 7.0.
%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);
| January 5, 2023 | NetBSD 9.4 |