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Basic C++ Mapping for Classes

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There is quite a bit to discuss here, so we will look at each item in turn.

Inheritance from Ice::Object in C++

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{zcode:slice}
["protected"] class TimeOfDay {
    short hour;         // 0 ? 23
    short minute;       // 0 ? 59
    short second;       // 0 ? 59
    string format();    // Return time as hh:mm:ss
};
{zcode}

Class Constructors in C++

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Note that single-parameter constructors are defined as explicit, to prevent implicit argument conversions.
By default, derived classes derive non-virtually from their base class. If you need virtual inheritance, you can enable it using the ["cpp:virtual"] metadata directive.

Class Operations in C++

Operations of classes are mapped to pure virtual member functions in the generated class. This means that, if a class contains operations (such as the format operation of our TimeOfDay class), you must provide an implementation of the operation in a class that is derived from the generated class. For example:

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Class Factories in C++

Having created a class such as TimeOfDayI, we have an implementation and we can instantiate the TimeOfDayI class, but we cannot receive it as the return value or as an out-parameter from an operation invocation. To see why, consider the following simple interface:

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{zcode:cpp}
Ice::CommunicatorPtr ic = ...;
ic?->addObjectFactory(new ObjectFactory, M::TimeOfDay::ice_staticId());
{zcode}

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Finally, keep in mind that if a class has only data members, but no operations, you need not create and register an object factory to transmit instances of such a class. Only if a class has operations do you have to define and register an object factory.

See Also

• Classes
• Smart Pointers for Classes
• C++ Mapping for Operations
• Asynchronous Method Invocation (AMI) in C++
• Dispatch Interceptors