Codesys add elements to a derived struct - struct

Question

Is it possible to add elements to an instance of struct.
TYPE StructBase:
STRUCT
Start : INT;
Complete : INT;
END_STRUCT
END_TYPE
StructDerived : StructBase;
StructDerived.StateInit : INT;
StructDerived.StateMoveFwd : INT;
The elements of StructDerived are going to be numbered in an 'enum' function.
On completion the StructDerived elements are used for a case statement.
The idea is to have a complete abstract function ready with the basic functionalities i require. When this function is extended, it should be clear where what to add. so all units in the machine for example all have the same lay-out.
What i was looking into was something like this:
TYPE BaseState:
STRUCT
EnumVal : INT;
Name : STRING;
END_STRUCT
END_TYPE
TYPE StructBase:
STRUCT
StateArray : ARRY [..] OF BaseState;
END_STRUCT
END_TYPE
StructDerived : StructBase;
StructDerived[0].Name := 'StateInit';
StructDerived[1].Name := 'StateMoveFwd';
So if i would use it in a case:
CASE AbortingState OF
StructDerived[0].EnumVal:
....
The 'Name' is logged for state tracking. Looks like a lot of work where something like a list or dictionary would do the trick.
Thanks for any advice in this matter.

Answer 1

First, you cannot use strings in CASE. Only ANY_NUM or ANY_BYTE general types. So, if you want to use enumeration, you will use it like this.
TYPE EN_STEPS: (
enStateInit,
enStateMoveFwd
);
END_TYPE
TYPE BaseState:
STRUCT
EnumVal : INT;
Step : EN_STEPS;
END_STRUCT
END_TYPE
GLOBAL_VAR
StateArray : ARRAY [1..c_TOTAL] OF BaseState :=
(EnumVal := 0, Step := enStateInit),
(EnumVal := 0, Step := enStateMoveFwd);
END_VAR
GLOBAL_VAR CONSTANT
c_TOTAL: INT := 2;
END_VAR
Then in program
VAR
currentStep : EN_STEPS;
END_VAR
CASE currentStep OF
StateArray[0].Step:
//do something
END_CASE
But this is not exactly clear why you are doing this. Looks like there is not a practical application for that. You could simply do
TYPE EN_STEPS: (
enStateInit,
enStateMoveFwd
);
END_TYPE
VAR
currentStep : EN_STEPS;
END_VAR
CASE currentStep OF
enStateInit:
//do something
END_CASE
The same thing.
Second, if you want to make a universal function that accepts a different number of elements you must use pointers. This is a general answer, if you edit your question and describe what you want to make in general, I will edit my answer and extend it with a solution.

Answer 2

Structured Text is a strongly typed language and it is not possible to dynamically add elements to a struct at runtime.
A data structure is not a function,therefor you should design a Function Block instead of a Struct if you intend to have a
complete abstract function ready with the basic functionalities i
require
"case of" instructions have one conditional variable which is checked against one or many conditional instructions (integer literals).
You can't use variables as your conditional instructions.
You can use inheritance to extend Structs and Function Blocks in order to create a hierarchy of different modules and instatiate them in different occasions for different purposes.