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SIZE — Size In Elements

Counts the elements of an array tag and stores the count in a DINT tag. Modeled on the SIZE instruction in Logix 5000® controllers.

The point of SIZE is to keep the array's length out of your logic. A loop written against a hardcoded TO 11 silently breaks the day someone resizes the tag to 20 elements; a loop written against a SIZE result keeps working.

SIZE(Samples, 0, Wrk_Count);

After this statement, Wrk_Count holds the number of elements in Samples — for an array created with size 12, that's 12 (elements Samples[0] … Samples[11]).

Operands​

NameType
arrayan array tag of any data type
dimensionthe literal 0
destinationDINT tag or DINT array element

array is the bare array tag — no index. dimension asks which dimension to measure; rungs supports single-dimension arrays only, so it must be the literal 0 (the first and only dimension).

Worked Example​

Average an array without ever hardcoding its length:

SIZE(Samples, 0, Wrk_Count);
Wrk_Sum := 0;
FOR Wrk_Index := 0 TO Wrk_Count - 1 DO
  Wrk_Sum := Wrk_Sum + Samples[Wrk_Index];
END_FOR;
Out_Average := Wrk_Sum / Wrk_Count;

Resize Samples in the tag editor and the loop follows along — no code change.

Rules​

  • Statement only. SIZE writes its result to the destination operand instead of returning a value, so Wrk_Count := SIZE(Samples, 0); is an error. Call it on its own line, then use the destination tag.

  • Whole array, not an element. SIZE(Samples[0], 0, Wrk_Count) is an error:

    SIZE array argument must reference an array tag, not an element access

  • Scalar tags are rejected. Pointing SIZE at a non-array tag produces:

    SIZE expects an array tag, but 'Count' is declared as scalar

  • Dimension is always the literal 0. A tag or any other number produces:

    SIZE dimension argument must be the literal 0

  • Destination must be DINT — a scalar tag or a single array element, not a whole array.

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