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NetBSD 6.1.5 - man page for vwarnx (netbsd section 3)

ERR(3)				   BSD 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 pro-
     gram to terminate with the status value given by the argument status.  It is often appropri-
     ate 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 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);

BSD					  March 21, 2001				      BSD


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