Structureswith optional fields shall be encoded as JSON objects as shown in Table 33.

Table 33– JSON Object Definition for a Structureswith Optional Fields

Name

Description

EncodingMask

A bit mask indicating what fields are encoded in the structure (see 5.2.7)

This mask is encoded as a JSON number.

The bits are sequentially assigned to optional fields in the order that they are defined.

<FieldName>

The fields structure encoded according to the rules defined for their DataType.

For the non-reversible form, Structureswith optional fields are encoded like Structures.

If a Structurewith optional fields is subtyped, the subtypes extend the EncodingMask (e)defined for the the parent.

The following is an example of a structure with optional fields using C++ syntax:

struct TypeA

{

Int32 X;

Int32* O1;

SByte Y;

Int32* O2;

};

O1 and O2 are optional fields where a NULL indicates that the field is not present.

Assume that O1 is not specified and the value of O2 is 0.

The reversible encoding would be:

{ "EncodingMask": 2 "X": 1, "Y": 2 }

Where decoders would assign the default value of 0 to O2 since the mask bit is set, however, the field was omitted (this is the behaviour defined for the Int32 DataType). Decoders would mark O1 as ‘not specified’.