Index Substructures and Fields

Use these guidelines when indexing substructures and fields for code generation:

 Reference substructure field values individually using dot notation

For example, the following MATLAB^® code uses dot notation to index fields and substructures:

...
substruct1.a1 = 15.2;
substruct1.a2 = int8([1 2;3 4]);

mystruct = struct('ele1',20.5,'ele2',single(100),
                  'ele3',substruct1);

substruct2 = mystruct;
substruct2.ele3.a2 = 2*(substruct1.a2);
...

The generated code indexes elements of the structures in this example by resolving symbols as follows:

Dot Notation	Symbol Resolution
substruct1.a1	Field a1 of local structure substruct1
substruct2.ele3.a1	Value of field a1 of field ele3, a substructure of local structure substruct2
substruct2.ele3.a2(1,1)	Value in row 1, column 1 of field a2 of field ele3, a substructure of local structure substruct2

 Reference field values individually in structure arrays

To reference the value of a field in a structure array, you must index into the array to the structure of interest and then reference that structure's field individually using dot notation, as in this example:

...
y = X(1).a % Extracts the value of field a 
           % of the first structure in array X
...

To reference all the values of a particular field for each structure in an array, use this notation in a for loop, as in this example:

...
s.a = 0;
s.b = 0;
X = repmat(s,1,5); 
for i = 1:5   
    X(i).a = i;   
    X(i).b = i+1; 
end

This example uses the repmat function to define an array of structures, each with two fields a and b as defined by s. See Define Arrays of Structures for Code Generation for more information.

 Do not reference fields dynamically

You cannot reference fields in a structure by using dynamic names, which express the field as a variable expression that MATLAB evaluates at run time (see Generate Field Names from Variables).