NAME    [Toc]    [Back]

     err, verr, errx, verrx, warn, vwarn, warnx, vwarnx - formatted error messages

SYNOPSIS    [Toc]    [Back]

     #include <err.h>

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

     void
     verr(int eval, const char *fmt, va_list args);

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

     void
     verrx(int eval, 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    [Toc]    [Back]

     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), a simple string, or NULL.  If the fmt argument is
not NULL,
     the formatted error message is output.

     In  the case of the err(), verr(), warn(), and vwarn() functions only, the
     error message string affiliated with the  current  value  of
the global
     variable  errno  is  output (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  counterpart  functions,  errx(),  verrx(), warnx(), and
vwarnx(), do not
     output the error message string, so the  output  looks  like
the following:

           progname: fmt

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

     The err(), verr(), errx(), and verrx() functions do not  return, but exit
     with the value of the argument eval.

EXAMPLES    [Toc]    [Back]

     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    [Toc]    [Back]

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

HISTORY    [Toc]    [Back]

     The err() and warn() functions first appeared in 4.4BSD.

CAVEATS    [Toc]    [Back]

     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);

OpenBSD     3.6                          August      8,      1997