MirBSD manpage: err(3), errx(3), verr(3), verrx(3), vwarn(3), vwarnx(3), warn(3), warnx(3)

ERR(3)                     BSD Programmer's Manual                      ERR(3)

NAME

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

SYNOPSIS

     #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

     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, 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

     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

     exit(3), perror(3), printf(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 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()
     functions.

     Always be sure to use the proper secure idiom:

           err(1, "%s", string);

MirBSD #10-current              August 8, 1997                               1