NAME

       errc, verrc, warnc, vwarnc — formatted error messages

LIBRARY

       Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

       #include <err.h>
       (See libbsd(7) for include usage.)

       void
       errc(int status, int code, const char *fmt, ...);

       void
       verrc(int status, int code, 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, followed by a colon (‘:’) character  and  a  space,
       are  output.   The  text  that  follows depends on the function being called.  The fmt specification (and
       associated arguments) may be any format allowed by printf(3) or NULL.  If the fmt argument is  not  NULL,
       the formatted error message is output.

       The  functions  all  output  an  error  message  string affiliated with an error value (see strerror(3)),
       preceded by a colon character and a space if fmt is not NULL.  That is, the output is as follows:

             progname: fmt: error message string

       if fmt is not NULL, or:

             progname: error message string

       if it is.

       The argument code is used as the error value instead of the current value of the global variable errno.

       In all cases, the output is followed by a newline character.

       The errc(), and verrc() functions do not return, but exit with the value of the argument status.

EXAMPLES

       Display the current errno information string and exit:

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

       Display an error message and exit:

             if (tm.tm_hour < START_TIME)
                     errx(1, "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(1, "%s", block_device);

SEE ALSO

       err(3) exit(3), perror(3), printf(3), strerror(3)

HISTORY

       The functions errc(), verrc(), warnc(), and vwarnc() first  appeared  in  FreeBSD  3.0,  NetBSD  7.0  and
       OpenBSD 5.6.

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 the stack,  leading  to  a  possible  security
       hole.   This  holds true even if the string has been built “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() family of functions.

       Always be sure to use the proper secure idiom:

             errc(1, 0, "%s", string);

Debian                                           April 23, 2014                                       errc(3bsd)