Pass the second array dimension into a function as a parameter

Engineering 🇬🇧
joanm
2022-05-04
2022-05-10

  • joanm - 2022-05-04

    Hello all,

    I am working on a program in which I have declared one two dimensional array like this:

    arrRawData : ARRAY [1..6,1..38] OF WORD;

    This array holds 38 words of raw data for 6 machine parts.

    I need to pass the second dimension array to a function:

    FUNCTION myDataReceiverFunction : BOOL
VAR_INPUT
  arrRawDataWords : ARRAY[1..38] OF WORD;
END_VAR
...

    But, when I try to call the function like this:

    myDataReceiverFunction(arrRawData[1]);

    The compiler alerts me that: Cannot convert type 'WORD' to type 'ARRAY[1..38]OF WORD'.

    I can use pointers, but, is there any easier syntax that would allow me to do this?

    Thank you in advance!

     

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  • joanm - 2022-05-04

    Answering myself just in case other people gets stuck here:

    I should have declared the array like this:

    arrRawData : ARRAY [1..6] OF ARRAY[1..38] OF WORD;

    Then my syntax does not make the compiler to go nuts.

    So it is solved.

     

  • ojz0r - 2022-05-05

    An explaination what is happening:
    When you declare the array it is basically a custom variable type and the input to the function needs to match exactly that even though the second dimension would look the same as a one dimensional array uncompiled.

     

  • tvm - 2022-05-05

    What's actually the difference between ARRAY [1..6,1..38] OF WORD, and ARRAY [1..6] OF ARRAY[1..38] OF WORD? It seems to me that they're the same thing. In either case arrRawData[1] should be an ARRAY [1..38] OF WORD. Other programming languages treat arrays in this way, is this just one of those Codesys quirks?

     

    • maretxa - 2022-05-05

      Hi,

      Not sure but :
      If you use ARRAY [1..6,1..38] OF WORD you can't use a variable to reach your table yourtable[1,1]

      But with ARRAY [1..6] OF ARRAY[1..38] OF WORD you can easly use a boucle FOR to search what you want in your table yourtable[1][1] OR yourtable[iIndex1][iIndex2]

       

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      • tvm - 2022-05-05

        Maybe I misunderstand what you're saying, but I regularly index 2 dimensional arrays with variables, for example:

        myArray: ARRAY[1..10,1..10] OF INT;

FOR i:= 1 TO 10 DO
    FOR j:= 1 TO 10 DO
        myArray[i,j]:= i;
    END_FOR
END_FOR
         

  • joanm - 2022-05-08

    @tvm it seems that you can't pass myArray[3] (from your example code) into a function that expects to get an array of 10 INTs.

    Not a big deal, but seems strange.

     

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  • ludecus

    ludecus - 2022-05-09

    While you need to work with array, there are two options:

    Declare a dynamic array size as input of the function (maybe it could require a FB instead)

    VAR_IN_OUT
    arrData : ARRY * OF WORD;
END_VAR

    During the compile the size of the dynamic array will be scaled.

    Or you could use a pointer

    VAR_INPUT
    parrData : POINTER TO WORD;
    nDataSize : UINT;
END_VAR

    Within the function or FB the pointer should be handled.

    At least both ways are more generic, if the array size has been changed.

     

  • joanm - 2022-05-10

    Thanks for your comment @ludecus, in any case, I'm very familiar with pointers and use them extensively in my daily basis, but it's not the solution I'm after now.

    Thanks again.

     

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