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ERR(3)			 BSD Library Functions Manual			ERR(3)

NAME
     err, verr, errx, verrx, warn, vwarn, warnx, vwarnx — formatted error mes‐
     sages

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 mes‐
     sage 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);

SEE ALSO
     exit(3), getprogname(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 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);

BSD				March 21, 2001				   BSD

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