Compare UDTs Value

PLCnext Engineer
1

Good morning all,

I'm in the process of developing my first project with the PLCNext and i run into some problems so far, i will make another post for the other problems but for this one i would like to ask the next:

Is it possible to compare somehow the value of two UDTs variables?

Let's say for example that i have created the next Data Types:

[b]TYPE

DatosAlarma : STRUCT
    
        Equipo : WSTRING := "";
        Texto : WSTRING := "";
        Activa : BOOL;
        Timestamp: LDATE_AND_TIME;
        Categoria : USINT := 0;
    
    END_STRUCT
    
    AlarmArray : ARRAY[0..99] of DatosAlarma;

END_TYPE[/b]

If i create two variables of the new type [b]"AlarmArray"[/b] and try to compare them in ST language to check if there's been any changes in the value of one of them, the software throws my an error:

[b]"The data type of the left operand ('AlarmArray') is not 'ANY_ELEMENTARY'. "[/b]

Is there any way two avoid this error and compare this two variables?

Thank you in advance!

Kind Regards,

Nacho
2

Unfortunately It’s not possible to do this as simply as you would like.

In languages like C++ you could overload the equality operator in your custom type, but that type of thing is currently not possible in IEC 61131 languages.
One solution would be to create a function that evaluates the equality of two variables of your custom type. You would need a separate function for every operator for every custom type, but if you only need a small number of these it might be a manageable (and neat) solution.
3

Hi martin,

Thank you for your quick response!

OK, that's a possible solution for me as i will only need (for the moment) to compare just one type of data types.

May i ask another question as we are already here:

Is it possible to create a variable of type ARRAY of "something" or a STRUCT directly in the variables tab of a function block without having to create a datatype for that?

Kind regards,

Nacho
4

No, unfortunately not. You will need to create a new data type for every array (type/length) and every struct. In PLCnext Engineer it is not possible to create these type definitions in a variable table.