Catching Exceptions

Exceptions are always caught by reference using the _var types. System exceptions must be caught by SystemException_var:

  // ok
  try {
    ...
    mico_throw (CORBA::UNKNOWN());
    ...
  } catch (CORBA::SystemException_var &ex) {
    ...
  }

  // wrong
  try {
    ...
    mico_throw (CORBA::UNKNOWN());
    ...
  } catch (CORBA::UNKNOWN_var &ex) {
    ...
  }

  // wrong
  try {
    ...
    mico_throw (CORBA::UNKNOWN());
    ...
  } catch (CORBA::Exception_var &ex) {
    ...
  }

Sometimes it is necessary to know exactly which system exception has been thrown:

  // ok
  try {
    ...
    mico_throw (CORBA::UNKNOWN());
    ...
  } catch (CORBA::SystemException_var &sys_ex) {
    if (CORBA::UNKNOWN *ukn_ex = CORBA::UNKNOWN::_narrow (sys_ex)) {
      // something1
    } else {
      // something2
    }
  }

  // wrong
  try {
    ...
  } catch (CORBA::UNKNOWN_var &ukn_ex) {
    // something1
  } catch (CORBA::SystemException_var &other_ex) {
    // something2
  }

In contrast to system exceptions a user exception X must be caught by X_var (i.e., not by UserException_var):

  // ok
  try {
    ...
    mico_throw (SomeExcept());
    ...
  } catch (SomeExcept_var &some_ex) {
    ...
  }

  // wrong
  try {
    ...
    mico_throw (SomeExcept());
    ...
  } catch (CORBA::UserException_var &usr_ex) {
    ...
  }

  // wrong
  try {
    ...
    mico_throw (SomeExcept());
    ...
  } catch (CORBA::Exception_var &ex) {
    ...
  }

If an exception is thrown but not caught MICO will print out a short description of the exception and terminate the process. On systems where g++ does not support exception handling throwing an exception will always result in such a message and termination of the process.