As in the case of Ice objects, a Dynamic Ice application may represent user exceptions in a native format that is not directly compatible with the Ice API. If the application needs to raise such a user exception to the Ice run time (so that it will be marshaled and sent back to the client), the exception must be wrapped in a subclass of Ice::UserException. The Dynamic Ice API provides a class to simplify this process:

{zcode:cpp}
namespace Ice {
    class UserExceptionWriter : public UserException {
    public:
        UserExceptionWriter(const CommunicatorPtr&);

        virtual void write(const OutputStreamPtr&) const = 0;
        virtual bool usesClasses() const = 0;

        virtual std::string ice_name() const = 0;
        virtual Ice::Exception* ice_clone() const = 0;
        virtual void ice_throw() const = 0;

        // ...
    };
    typedef ... UserExceptionWriterPtr;
}
{zcode}

A subclass of UserExceptionWriter is responsible for supplying a communicator to the constructor, and for implementing the following methods:

• void write(const OutputStreamPtr&) const
  This method is invoked when the Ice run time is ready to marshal the exception. The subclass must marshal the exception using the encoding rules for exceptions.

• bool usesClasses() const
  Return true if the exception, or any base exception, contains a data member that is an object by value.

• std::string ice_name() const
  Return the Slice name of the exception.

• Ice::Exception* ice_clone() const
  Return a copy of the exception.

• void ice_throw() const
  Raise the exception by calling throw *this.

See Also

• Intercepting Object Insertion and Extraction in C++
• Data Encoding for Exceptions