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]).

OperandsCopy Anchor Link

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 ExampleCopy Anchor Link

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.

RulesCopy Anchor Link

• 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.

• The whole array, or its first element. SIZE(Samples, 0, Wrk_Count) and SIZE(Samples[0], 0, Wrk_Count) mean the same thing. Any other element is an error, because there is no such thing as the size of a run starting part-way along:

  SIZE array argument must be the array itself or its first element, such as 'Samples' or 'Samples[0]'

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

  SIZE array needs an array tag, but 'Count' holds one value

• 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. The Ladder form takes a REAL destination as well; this one does not.

In LadderCopy Anchor Link

SIZE is on the Array tab in Ladder too, with the same three operands. See SIZE in Ladder.