Manual Pages  — COM_ERR

The error table is registered with the com_err library by calling its initialisation function defined in its header file. The initialisation function is generally defined as initialize_<name>_error_table(), where name is the name of the error table.

If a thread-safe version of the library is needed initialize_<name>_error_table_r() that internally calls initialize_error_table_r() instead be used.

Any variable which is to contain an error code should be declared <name>_error_number where name is the name of the error table.

        #include <stdio.h>
        #include <stdarg.h>
        #include <syslog.h>

        #include "test_err.h"

        void
        hook(const char *whoami, long code,
                const char *format, va_list args)
        {
                char buffer[BUFSIZ];
                static int initialized = 0;

                if (!initialized) {
                        openlog(whoami, LOG_NOWAIT, LOG_DAEMON);
                        initialized = 1;
                }
                vsprintf(buffer, format, args);
                syslog(LOG_ERR, "%s %s", error_message(code), buffer);
        }

        int
        main(int argc, char *argv[])
        {
                char *whoami = argv[0];

                initialize_test_error_table();
                com_err(whoami, TEST_INVAL, "before hook");
                set_com_err_hook(hook);
                com_err(whoami, TEST_IO, "after hook");
                return (0);
        }