The String and DDS_KeyedString types are appropriate for simple text-based applications. The DDS_Octets and DDS_KeyedOctets types are appropriate for applications that perform their own custom data serialization, such as legacy applications still in the process of migrating to dds. In most cases, string-based or structured data is preferable to opaque data, because the latter cannot be easily visualized in tools or used with content-based filters (see DDS.ContentFilteredTopic).

The built-in types are very simple in order to get you up and running as quickly as possible. If you need a structured data type you can define your own type with exactly the fields you need in one of two ways:

Managing Memory for Builtin Types

When a sample is written, the DataWriter serializes it and stores the result in a buffer obtained from a pool of preallocated buffers. In the same way, when a sample is received, the DataReader deserializes it and stores the result in a sample coming from a pool of preallocated samples.

For builtin types, the maximum size of the buffers/samples and depends on the nature of the application using the builtin type.

You can configure the maximum size of the builtin types on a per-DataWriter and per-DataReader basis using the DDS.PropertyQosPolicy in DataWriters, DataReaders or Participants.

The following table lists the supported builtin type properties to configure memory allocation. When the properties are defined in the DomainParticipant, they are applicable to all DataWriters and DataReaders belonging to the DomainParticipant unless they are overwrittem in the DataWriters and DataReaders.

The previous properties must be set consistently with respect to the corresponding *.max_size properties that set the maximum size of the builtin types in the typecode.

Typecodes for Builtin Types

The typecodes associated with the builtin types are generated from the following IDL type definitions:

module DDS {
     struct String {
         string value;
     };
 
     struct KeyedString {
         string key;
         string value;
     };
 
     struct Octets {
         sequence value;
     };
 
     struct KeyedOctets {
         string key;
         sequence value;
     };
 };

The maximum size of the strings and sequences that will be included in the type code definitions can be configured on a per-DomainParticipant-basis by using the properties in following table.

For more information about the built-in types, including how to control memory usage and maximum lengths, please see the "Data Types and DDS Data Samples" chapter in the User's Manual .