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ERR(3)                     Library Functions Manual                     ERR(3)

NAME
     err, verr, errx, verrx, errc, verrc, warn, vwarn, warnx, vwarnx, warnc,
     vwarnc -- 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
     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);

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 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(), 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.  The errc() and
     warnc() functions first appeared in FreeBSD 3.0 and NetBSD 7.0.

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);

NetBSD 7.1.2                   January 16, 2014                   NetBSD 7.1.2