Embedded IDE Link™ CC

Structure Objects — Their Methods and Properties

When you create an object that accesses a structure symbol declared in your source code, the object constructor createobj returns a structure object. createobj uses the information in your source code to set the properties of the object appropriately to match the code. Within the properties and their values you find all the information about the symbol, so that MATLAB understands how to handle the symbol in your MATLAB workspace.

Like memory and register class objects, structure objects do not inherit properties from a parent class.

Properties of Structure Objects

Object properties can include both properties that the object inherits from its superclass, if any, and some properties that are unique to the class itself. For this reason, many objects in Embedded IDE Link CC share common properties; as you use the objects you will become familiar with the common and special properties for each.

Back to Top

Methods of Structure Objects

Like properties, methods for objects may come from the superclass or derive only from the class itself. For example, the cast and convert methods do not appear in all objects; listing them here indicates that the object does not inherit these methods but provides them itself.

Back to Top

Working with Structure Objects

structure objects present some unexpected behavior when you try to access the elements referred to by the structure object. Consider the following example that creates a structure object and accesses the members.

Suppose we have a structure variable in CCS:

creal32_T mw_output[512]; 

In MATLAB, create an object to mw_output. The size (512) is correctly propagated to the structure object:

a = createobj(cc,'mw_output');

STRUCTURE Object stored in memory: 
  Symbol name             : mw_output
  Address                 : [ 2147652624 0]
  Address units per value : 8 au
  Size                    : [ 512 ]
  Total Address Units     : 4096 au
  Array ordering          : row-major 
  Members                 : 're', 'im'

If you now look at a member re of the structure the size is not 512 any more. It returns a size of 1.

a.member.re

NUMERIC Object stored in memory: 
  Symbol name             : re
  Address                 : [ 2147652624 0]
  Data type               : float
  Word size               : 32 bits
  Address units per value : 4 au
  Representation          : float
  Size                    : [ 1 ]
  Total address units     : 4 au
  Array ordering          : row-major
  Endianness              : little

Now look at another member. Again, the size is 1.

a.member.im

NUMERIC Object stored in memory: 
  Symbol name             : im
  Address                 : [ 2147652628 0]
  Data type               : float
  Word size               : 32 bits
  Address units per value : 4 au
  Representation          : float
  Size                    : [ 1 ]
  Total address units     : 4 au
  Array ordering          : row-major
  Endianness              : little

The size of the members cannot reflect the size of the structure object.

If you have

  struct tag {
    int a;
    int b;
  } mystruct[10];

In memory, the values are arranged in the following way:

memory1: mystruct[0] -> member a value

memory2: mystruct[0] -> member b value

memory3: mystruct[1] -> member a value

memory4: mystruct[1] -> member b value

...

memory19: mystruct[9] -> member a value

memory20: mystruct[9] -> member b value

Therefore, when you do the following functions:

structobj = createobj(cc,'mystruct')
aobj = structobj.member.a;

and aobj.size is same as structobj.size, you will be reading the wrong set of values, as shown by the example that shows the structure memory values and layout.

Setting the value of aobj to 1 provides a safe way to allow you to access the members of a structure.

The most reliable way to access a structure objects members is to read the structure into MATLAB and reference the members there. In the next code example you see how to do this.

x = createobj(cc,'m')

STRUCTURE Object stored in memory: 
  Symbol name             : m
  Address                 : [ 13544 0]
  Address units per value : 12 au
  Size                    : [ 2 ]
  Total Address Units     : 12 au
  Array ordering          : row-major 
  Members                 : 'a', 'b'

out = read(x)

out = 

1x2 struct array with fields:
    a
    b

out(1)

ans = 

    a: 3
    b: 1.5000

out(2)

ans = 

    a: 12648430
    b: 1.7724e-038

read(x,'a')


ans =

           3    12648430

Use the read function to return the value of a for the first element in the structure.

read(x,1,'a')

ans =

     3

read(x,2,'a')

ans =

    12648430

Back to Top

Function Objects — Their Methods and Properties

Type Objects — Their Methods and Properties