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ERR(3)			     Library Functions Manual			  ERR(3)

NAME
     err,  verr,  errc,  verrc,  errx, verrx, warn, vwarn, warnc, vwarnc, warnx,
     vwarnx, err_set_exit, err_set_file -- formatted error messages

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <err.h>

     void
     err(int eval, const char *fmt, ...);

     void
     err_set_exit(void (*exitf)(int));

     void
     err_set_file(void *vfp);

     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, ...);

     #include <stdarg.h>

     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);

DESCRIPTION
     The err() and warn() family of functions display a formatted error  message
     on  the  standard	error  output,	or  on	another file specified using the
     err_set_file() function.  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 printf(3)-like formatted error message is output.  The output
     is terminated by a newline character.

     The err(), errc(), verr(), verrc(), warn(), warnc(), vwarn(), and	vwarnc()
     functions append an error message obtained from strerror(3) based on a sup-
     plied  error  code  value or the global variable errno, preceded by another
     colon and space unless the fmt argument is NULL.

     If the kernel returned an extended error string in addition  to  the  errno
     code, the err() function prints the string with interpolated values for pa-
     rameters,	as  provided to the corresponding invocation of EXTERROR(9).  If
     the extended error string was not provided, but extended error  information
     was,  or  even  if string was provided and the EXTERROR_VERBOSE environment
     variable is present, an additional report is printed.  The report	includes
     at  least	the category of the error, the name of the source file (if known
     by the used version of libc), the source line number, and	parameters.   If
     the  EXTERROR_VERBOSE  environment  variable is present and set to "brief",
     the report adds only the name of the source file (if known by the used ver-
     sion of libc) and the source line number.	The format of the printed string
     is not contractual and might be changed.

     In the case of the errc(), verrc(), warnc(), and  vwarnc()  functions,  the
     code argument is used to look up the error message.

     The  err(),  verr(),  warn(), and vwarn() functions use the global variable
     errno to look up the error message.

     The errx() and warnx() functions do not append an error message.

     The err(), verr(), errc(), verrc(), errx(), and verrx()  functions  do  not
     return,  but  exit  with the value of the argument eval.  It is recommended
     that the standard values defined in sysexits(3) be used for  the  value  of
     eval.   The err_set_exit() function can be used to specify a function which
     is called before exit(3) to perform any necessary cleanup; passing  a  null
     function	pointer   for	exitf  resets  the  hook  to  do  nothing.   The
     err_set_file() function sets the output stream used by the other functions.
     Its vfp argument must be either a pointer to an open stream  (possibly  al-
     ready  converted  to  void  *)  or a null pointer (in which case the output
     stream is set to standard error).

EXAMPLES
     Display the current errno information string and exit:

	   if ((p = malloc(size)) == NULL)
		   err(EX_OSERR, NULL);
	   if ((fd = open(file_name, O_RDONLY, 0)) == -1)
		   err(EX_NOINPUT, "%s", file_name);

     Display an error message and exit:

	   if (tm.tm_hour < START_TIME)
		   errx(EX_DATAERR, "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(EX_OSFILE, "%s", block_device);

     Warn of an error without using the global variable errno:

	   error = my_function();  /* returns a value from <errno.h> */
	   if (error != 0)
		   warnc(error, "my_function");

SEE ALSO
     exit(3), fmtmsg(3), printf(3), strerror(3), sysexits(3)

STANDARDS
     The err() and warn() families of functions are  BSD  extensions.	As  such
     they  should not be used in truly portable code.  Use strerror() or similar
     functions instead.

HISTORY
     The  err()  and  warn()  functions   first   appeared   in   4.4BSD.    The
     err_set_exit()  and err_set_file() functions first appeared in FreeBSD 2.1.
     The errc() and warnc() functions first appeared in FreeBSD 3.0.

FreeBSD ports 15.quarterly	February 23, 2026			  ERR(3)

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