Introduction to the Type System

A user data type is any custom type that your application defines for use with Connext DDS. It may be a structure, a union, a value type, an enumeration, or a typedef (or language equivalents).

Your application can have any number of user data types. They can be composed of any of the primitive data types listed below or of other user data types.

Only structures, unions, and value types may be read and written directly by Connext DDS; enums, typedefs, and primitive types must be contained within a structure, union, or value type. In order for a DataReader and DataWriter to communicate with each other, the data types associated with their respective Topic definitions must be identical.

• octet, char, wchar
• short, unsigned short
• long, unsigned long
• long long, unsigned long long
• float
• double, long double
• boolean
• enum (with or without explicit values)
• bounded and unbounded string and wstring

The following type-building constructs are also supported:

• module (also called a package or namespace)
• pointer
• array of primitive or user type elements
• bounded/unbounded sequence of elements1Sequences of sequences are not supported directly. To work around this constraint, typedef the inner sequence and form a sequence of that new type.—a sequence is a variable-length ordered collection, such as a vector or list
• typedef
• bitfield2Data types containing bitfield members are not supported by DynamicData. [RTI Bug # 12638]
• union
• struct
• value type, a complex type that supports inheritance and other object-oriented features

To use a data type with Connext DDS, you must define that type in a way the middleware understands and then register the type with the middleware. These steps allow Connext DDS to serialize, deserialize, and otherwise operate on specific types. They will be described in detail in the following sections.

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