To program a user defined IECArray, it is recommended to use the complete sample struct - provided here - as a template. The sample function block shows how to use an int array in C#.
The implementation of an IECArray needs the PLCnext specific attributes, Array() ArrayDimension() and DataType().
Furthermore the StructLayout() with the "Anchor" field as FieldOffset() provides a full implementation, including the ability to use the index operator.
In some cases of complex datatypes the sizeof() keyword does not return the correct size.
Following example shows how to calculate the size of a struct as array elements:
| Variable Name | Datatype | size |
|---|---|---|
| index | int | 4 Byte |
| value | double | 8 Byte |
| txt | IecString80 | 86 Byte (calculation) |
- 6 Byte padding (8 Byte aligment due to the double data type) Struct size = 104
The alignment always depends on the biggest variable. The IECString itself is only a 2 Byte aligned struct, therefore in this example the double is the leading element and the structure becomes the 8 Byte alignment.
The [Execution] method __Process() demonstrates two jobs:
- Calculate the average value of the given array's elements.
- Compare the current array content to its content of the previous FB call.