Delphi xe3 vcl to firemonkey array issue

Question

When converting from VCL to Firemonkey in Delphi, I have the following issue: In VCL I have the following array: Tcarray=array[1..$04000000] of Tcoordinate; - This works fine.

However, declaring the same array in Firemonkey I get an exception about stack overflow at 0x00.. My only solution so far is to minimize the array to [1..40000].

Why is this? Any solution?

The VCL code is as follow

unit ptypes;

interface
uses windows,vcl.Graphics,Vcl.Imaging.jpeg,Vcl.Imaging.GIFImg,system.Types;

type
Tcoordinate=packed record
x,y:double;
end;

Tcarray=array[1..$04000000] of Tcoordinate;

Tpoly=packed record
   n:longint;
   c:Tcarray;
end;

It will be called like this:

procedure TForm12.Button2Click(Sender: TObject);
var
   poly:Tpoly;
begin
with poly do
begin
    c[1].x:=100; c[1].y:=100;
    c[2].x:=400; c[2].y:=100;
    c[3].x:=400; c[3].y:=400;
    c[4].x:=250; c[4].y:=550;
    c[5].x:=100; c[5].y:=400;
    n:=5;
end;

This works fine in VCL but in FM it breaks with the following error: "Project FMtest.exe raised exception class $C00000FD with message 'stack overflow at 0x00af69e7'.

You need to edit your post to add the actual code (the full declarations of the type, the code that declares the actual array, and the code that uses it), along with the exact error message you're getting with the exception, for both versions of the code if you want us to help. A vague description of the problem is probably not going to be enough, because what you're describing shouldn't be happening. — Ken White

RRUZ RRUZ · Accepted Answer · 2013-05-22T17:38:42

This stack overflow occurs because you are creating a very large local variable poly (of 1.073.741.828 bytes ¡¡¡¡) and the stack (the place where the local variables are stored) has a limited size.

You can avoid this issue redeclarating your types in this way

PCArray=^Tcarray;
Tcarray=array[1..$04000000] of Tcoordinate;


Tpoly=packed record
   n:longint;
   c:PCArray;
end;

And use like so

var
   poly   : Tpoly; //now poly only uses 8 bytes of the stack space
   points : integer;
begin
  points:=5;
  GetMem(poly.c,sizeof(Tcoordinate)*points);
  try
    with poly do
    begin
      c[1].x:=100; c[1].y:=100;
      c[2].x:=400; c[2].y:=100;
      c[3].x:=400; c[3].y:=400;
      c[4].x:=250; c[4].y:=550;
      c[5].x:=100; c[5].y:=400;
      n:=points;
    end;
  finally
    FreeMem(poly.c);
  end;
end;

Delphi xe3 vcl to firemonkey array issue

1 Answers