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plc st structured-text twincat iec61131-3

How to pass variable type as an argument to an function in IEC61131-3 structured text (TwinCAT3)?

发布于 2021-01-21 09:44:06

This is what I would like to have (this is a constructor for FB object):

METHOD FB_init : BOOL
    VAR_INPUT
        bInitRetains : BOOL;
        bInCopyCode : BOOL;

        //My variables:
        typeOfVariable : TYPE; // This obviously doesn't work 
    END_VAR

size := 1;
myArray := __NEW(typeOfVariable, size); // Create dynamic array with 'typeOfVariable' variables.

END_METHOD
  • In this method I would pass to the parameter typeOfVariable for example REAL and the method would create array of REAL variables with size 1.
  • I need to know what type I declare typeOfVariable so it can store the data about type of another variable.

  • Working example is the __NEW() method for dynamically creating array.

  • This method takes in a argument such as REAL or INT.

This is the code for it:

myArray := __NEW(REAL, 10); //Create array with type REAL variables with the size of 10
Questioner
Jakub Szlaur
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Filippo Boido 2021-01-22 02:53:30

OK, here a small example how you could tackle this problem:

Create an Enum first:

TYPE E_Type :
(
    eNO_TYPE := 0,
    eINT,
    eREAL
);
END_TYPE

Use it in a switch case:

METHOD createArray : POINTER TO BYTE
VAR_INPUT
    eType : E_Type;
    size : UINT;
END_VAR

CASE eType OF
    eINT:
        //Remember to __DELETE
        createArray := __NEW(INT, size);
    eREAL:
        createArray := __NEW(REAL, size);
END_CASE

Check for Null-Pointer and remember to __Delete when you don't need the array anymore.

Jakub Szlaur 2021-01-21 21:31:44

this is actually implementation I am using now. But I am still curios if there is another way to do it - therefor I put this question here in hope it can be answered :)

Jakub Szlaur 2021-01-21 21:34:33

+1 but I won't accept it. Would you consider giving the question also +1? It has been never asked on SO so far (in context of IEC61131-3) ... And I really hope someone can find a solution or explanation why it can't be done.

Filippo Boido 2021-01-21 22:59:44

Simple answer: You can't pass the Type directly, the compiler won't allow it. But you can go around it with implementations like the one above..It must be said that when developing code for industrial machines you should be aware of the special context you are in.Creating dynamic memory is used in the rarest occasions and should be avoided when not necessary. You have a very similar philosophy in the ADA language (83 or 95) widely used in military and civilian aviation.

Jakub Szlaur 2021-01-22 12:03:29

Ah okay thank you! Didn't know that! :)

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