Dynamical arrays

Are you using Delphi4, if so, you can just create the array by:

mArray:Array of MyRecordType;

With no range defined, you can increase the size dynamically in code.

Sorry,

mArray=Array of MyRecordType

vfrc,

here is the example I once got from inter :

Good day(or night) friends,

I'd like to give an example about dynamic allocation and range checking off...

Simply start with a new form and paste the following code and link the FormCreate method to the
one below.

//CODE BEGINS
unit Unit1;

interface

uses

Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

type

TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

type

PTestRec = ^TTestRec;
TTestRec = packed record
x : integer;
y : array[0..0] of char;
end; var
Form1: TForm1;

implementation

{$R *.DFM}

// turn range checking off so that we can access ttestrec.y[0...n]
{$R-} procedure TForm1.FormCreate(Sender: TObject);
var
p : PTestRec; //declare a pointer
i : integer; begin
GetMem(p, sizeof(TTestRec) + 20);
try
i :=5;
StrCopy(p.y, 'hello there');
Caption := StrPas(PChar(@(p.y[i])));
finally
FreeMem(p, sizeof(TTestRec) + 20);
end; end;

end.

// CODE ENDS

WHAT IS UP

--------------

Our record decleration is as follows(just an example)

PTestRec = ^TTestRec;

TTestRec = packed record
x : integer;
y : array[0..0] of char;
end;

Now assume that, I want to place a null terminated string in y and feed to some function. Now let's analyze the code at
formcreate(follow my comments)

{$R-}
procedure TForm1.FormCreate(Sender: TObject);
var
p : PTestRec;
i : integer; begin
// now this is dynamic allocation. By doing this
// I have a record at p which indirectly means as follows
// TTestRec = packed record
// x : integer;
// y : array[0..20] of char;
// end;
GetMem(p, sizeof(TTestRec) + 20);
try
i :=5; // we should use a variable to address the p.y[i]
// note that p.y[1] produces and error at COMPILE TIME
StrCopy(p.y, 'hello there'); //no GPFault! we succeeded
Caption := StrPas(PChar(@(p.y[i]))); //forms caption should be 'there'
finally
FreeMem(p, sizeof(TTestRec) + 20);
end; end;

To test it put a break point at formcreate and run the program. Step and debug the p and its members...

So, is it clear?
Regards, Igor

Regards, Zif.

ps. all thanks to inter.

hi vfcr,

here a sample in old pascal-code(simple List), it also works in delphi-code

type
  YourRecord = record
                        YourRecordEntries;                  
                     end;


type
   YourRecordPointer = ^YourRecordList;
   YourRecordList = Record
                                 YR : YourRecord;
                                  Next : YourRecordPointer;
                              end;
var
  rootptr : YourRecordPointer = nil; {holds the start of the list}
  tmpptr : YourRecordPointer = nil; {temporary for free use (search, create, delete)}
  topptr  : YourRecordPointer = nil; {holds the top of the list}


procedure addrecord(ARecord : YourRecord);
begin
   new(tmpPtr);
   tmpptr^.YR := ARecord;
   tmpptr^.next := nil;
   { First Entry ?}
   if rootptr = nil then rooptr := tmpptr;
   if  topptr = nil then
      topptr := tmpptr
   else
   begin {No First Entry}
     topptr^.next := tmpptr;
     topptr := tmpptr;
  end;
end;

procedure deletedynlist;
begin
  tmpptr := rootptr;
  while tmpptr <> nil do
  begin
    rootptr := tmpptr^.next;
    dispose(tmpptr);
    tmpptr := rootptr;
  end;
end;

there can be more procedures as sortlist or deleteentry or searchrecord and so on

meikl

hi vfrc,

i forget the topptr

procedure deletedynlist;
begin
  tmpptr := rootptr;
  while tmpptr <> nil do
  begin
    rootptr := tmpptr^.next;
    dispose(tmpptr);
    tmpptr := rootptr;
  end;
  Topptr := nil;
end;

meikl

Another way is by the use of TList (available even for Delphi 1.0)

http://www.delumpa.com/

Look in the tips section to learn how to use dynamic arrays if you don't have Delphi 4.

But if you HAVE Delphi 4, please please please use it's dynamic arrays. You can dynamically change the array size by using SetLength(array,arrayLen)...

Regards, Madshi.

Some of us are handicapped!!  Some of us only have Delphi 2!! (Are we classified as Delphi Gimps?)   :)

Yes, you are...   :-)

Hello?

Tim.