elog.c

 * not available). Used before ereport/elog can be used
 * safely (memory context, GUC load etc)
 */
void
write_stderr(const char *fmt,...)
{
	va_list		ap;

	fmt = _(fmt);

	va_start(ap, fmt);
#ifndef WIN32
	/* On Unix, we just fprintf to stderr */
	vfprintf(stderr, fmt, ap);
#else

	/*
	 * On Win32, we print to stderr if running on a console, or write to
	 * eventlog if running as a service
	 */
	if (pgwin32_is_service())	/* Running as a service */
	{
		char		errbuf[2048];		/* Arbitrary size? */

		vsnprintf(errbuf, sizeof(errbuf), fmt, ap);

		write_eventlog(EVENTLOG_ERROR_TYPE, errbuf);
	}
	else
		/* Not running as service, write to stderr */
		vfprintf(stderr, fmt, ap);
#endif
	va_end(ap);
}