Initialize Array of Custom Types in Structured Text Syntax

Question

In my project I have a type like:

TYPE myDataStruct :
STRUCT
    A : UINT;
    B : WORD;
    C : REAL;
    D : Custom_Obj;
END_STRUCT
END_TYPE

And I need to keep an array of this type for persistent memory. I can't just use VAR RETAIN because this particular piece of memory needs to persist through a download. The controller I am using has a way to do this but in order for it to work I need to be able to set the array equal to an initial value. So if I have declared

myarray := ARRAY[0..20] OF myDataStruct;

How do I then initialize this array to a blank array? What is the equivalent of new in other languages?

I have guessed

myarray := [21(A := 0,
               B := '',
               C := 0.0,
               D := ??? )];

But that doesn't appear to be right. It could be simplified if there were only one level deep of custom structs and for this application I could do that. However, I still don't think I have the syntax right.

Did you get your answer? – Sergey Romanov Feb 03 '19 at 04:19 — Sergey Romanov, Feb 03 '19 at 04:19

score 2 · Accepted Answer · answered Feb 01 '19 at 07:06

What is the equivalent of new in other languages?

The analog of this is

VAR
    EmptyArray  : ARRAY[0..20] OF myDataStruct;
END_VAR

If you want to pre-populate it with default values

VAR
    EmptyArray  : ARRAY[0..20] OF myDataStruct := [
        (A := 100, B := 200, С := 0.0, D := ???),
        (A := 34, B := 45, С := 0.1, D := ???),
        ..... etc
    ];
END_VAR

For CoDeSys 2.3 delete [ and ].

What you have to understand that EmptyArray is not a prototype of data you need but already initialized variable.

score 1 · Answer 2 · answered Feb 01 '19 at 06:33

There is no way to initialize it in "x = new struct()" way. You also can't assign the whole array in the code with something like myarray = [1, 2, 3] etc, as far as I know.

If you just want to set it empty with values like 0, '', etc, then there are two ways that I would use:

1. Use MEMSET function to set all bytes to 0

Link to the online help

//Something like
MemSet(
    pbyBuffer   := ADR(myarray),    //Address of the variable
    byValue     := 0,               //Byte that address is filled with
    dwSize      := SIZEOF(myarray)  //How many bytes? (variable size)
)

2. Create a dummy variable and assign it to the myarray

The variable is always initialized to zeros, so EmptyArray values are all 0/empty etc.

VAR
    EmptyArray  : ARRAY[0..20] OF myDataStruct;
END_VAR

//In the code
myarray := EmptyArray;

I hope I understood your question correctly.

Initialize Array of Custom Types in Structured Text Syntax

2 Answers2