Stan wrote:
> I'd like to use routine R in any of several projects. But those
> projects, while using arrays of type extended, define the arrays of
> different lengths, e.g., one might define MyArray : array[1..500] of
> extended while another might have AnotherArray : array[1..750] of
> extended.
>
> I'd like to include my UnitR into the "uses" of any of my projects,
> and not have a fixed array size in R's code that I'd have to change to
> match whatever the calling routine is sending.
Then R should receive an open array of Extended.
function R(const Data: array of Extended): Extended;
var
J: Cardinal;
begin
Assert(Length(Data) > 0);
for J := Low(Data) to High(Data) do
// Do stuff with Data[J]
end;
var
a: array[0..1] of Extended;
b: array[3..6] of Extended;
c: array of Extended;
begin
R(a);
R(b);
R(c);
end.
> It seems I should pass the array to R using a pointer to the
> calling routine's array and an integer parameter indicating the number
> of elements in the array. My question(s):
>
> 1. Is this the correct approach? And if so...
Well, it's _a_ correct approach. Not the ideal one for Delphi, though.
> 2. What is the syntax for (1) the calling routine, and (2) routine R.
> For example, if R (which is an object) has a method, ComputeValue,
> should it be defined as
> function ComputeValue ( P : pointer; N : integer ) : extended;
No. You know what P will point to -- an Extended -- so let the compiler
know as well. The more the compiler knows about your program, the more
it can help you write it properly.
function ComputeValue(const P: PExtended; const N: Cardinal): Extended;
> and if so, how would I access element [J] of the calling program's
> array?
var
Data: PExtended;
J: Cardinal;
begin
Data := P;
J := 0;
while J <= N do begin
// Do things with Data^;
Inc(Data);
Inc(J);
end;
end;
type
TExtendedArray = array[0..MaxInt div SizeOf(Extended) - 1] of Extended;
PExtendedArray = ^TExtendedArray;
var
Data: PExtendedArray;
J: Cardinal;
begin
Assert(N > 0);
Data := PExtendedArray(P);
for J := 0 to Pred(N) do
// Do stuff with Data[J]
end;
> How would the calling program pass its array, say MyArray :
> array[1..500] of extended, to R? Would it be:
> MyResult := ComputeValue( @MyArray, 500 ); ??
That could work. I'd write it like this:
Result := ComputeValue(@Data[1], Length(Data));
--
Rob
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