SQLConnect(hdbc, "hostname/dbname", SQL_NTS, "user", SQL_NTS, "pass", SQL_NTS);
SQLConnect(hdbc, "hostname:dbname", SQL_NTS, "user", SQL_NTS, "pass", SQL_NTS);

// just as jdbc format...
SQLConnect(hdbc, "odbc:db2://hostname/dbname", SQL_NTS, "user", SQL_NTS, "pass", SQL_NTS);