IDL Exception Type Definition
IDL Exception Type Constructor
An IDL exception maps to a C++ class that derives from the standard UserException class which is defined in the CORBA module and which contains the exception's data. The derived class is like a variable-length struct and each exception member must handle its own storage. The copy constructor, assignment operator, and destructor automatically copy or free the storage associated with the exception.
The UserException class is derived from CORBA::Exception, which is defined in the CORBA namespace:
//C++
class UserException : public Exception {
. . .
};
The Exception base class can only be instantiated as part of an instance of a derived class.
The following exception in IDL:
//IDL
exception Discard {
string logic;
short x;
}
This example maps to the following C++ code:
//C++
class Discard : public CORBA::UserException {
public:
CORBA::String_mgr logic;
CORBA::Short x;
Discard(const char* _logic,
const CORBA::Short& _x);
Discard( );
static Discard* _narrow(CORBA::Exception *e);
}
The C++ mapping defines a constructor that has one parameter for each exception member. The constructor initializes the exception members to the specified values. String exception types require a const char* parameter.
In the example, the constructor has two parameters, Logic and x, one for each field in the exception. The exception can be thrown as follows:
// C++
throw Discard("Explanation", 10)
The exception classes support the _narrow( ) static member function. The function's parameter is a pointer to an object of class CORBA::Exception. It is the base class of all user-defined and system exceptions. You can call CORBA::Exception as follows:
//IDL
interface Customer
exception Reject {
. . .
};
Account newCustomer( ) raises (Reject);
}
// C++
Exception* e = . . .
// Narrow e so it is a Customer::Reject exception
if (Customer::Reject* r = Customer::Reject::narrow(e))
else . . .
The default constructor performs no member initialization. The copy constructor, assignment operator, and destructor automatically copy or free the storage related to the exception.