What are open array parameters in Pascal?

Overview

Open array parameters are arrays passed as parameters with an unspecified length.

Note: To get the length (or last index) of open array parameters inside a function or a procedure, we can use the High() function.

Return value

If an empty array (array with size 0) is passed as an open array parameter, the high() function returns -1.

Parameters

Open array parameters can be passed by reference, value, or constant parameters.

Example

The code snippet below demonstrates the use of an open array parameter:

{$MODE DELPHI}
Function Sum (arr : Array of integer) : integer;  
Var I : longint;  
    Temp : integer;  
begin  
  Temp := arr[0];  
  For I := 1 to High(arr) do 
    Temp := Temp + arr[I];  
  Sum := Temp;  
end;
Var  
  arr : Array [1..6] of integer;
  arr2 : Array [1..10] of integer;
  I : integer;
begin
  For I := 1 to 6 do 
    arr[I] := I;
  Writeln('Sum of elements of arr = ',Sum(arr));
  
  For I := 1 to 10 do 
    arr2[I] := I;
  Writeln('Sum of elements of arr = ',Sum(arr2));
end.

Output

Sum of elements of arr = 21
Sum of elements of arr = 55

Code explanation

  • Line 3: We declare a Sum function.
    • The Sum function takes arr as an open array parameter. This means that the size of arr is not declared in the definition of Sum.
  • Line 20: We pass an array arr of size 6 to the Sum function as an open array parameter.
  • Line 24: We pass an array arr2 of size 10 to the Sum function as an open array parameter.

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