dynamic array as type in delphi/pascal object

Question

I have a unit in which there are multiple variables that has to be same sized vectors.

However I do not know the length of this array before i parse the file.

So I want to have a dynamic array that is "global" for the whole unit and then i can

The code below shows the issue as well as the solution I have now. The solution I have now is to assign a maximum value to be the length of the array.

unit xyz;
interface 

uses
abc

const
maxval=50;

type
vectorofdouble = [1...maxval] of double;  // I want to change this to dynamic array

type
  T_xyz = object

  public
    NP: integer;
  private
    var1: vectorofdouble;        
    var2: vectorofdouble;        
   public
    number: integer;       
    var3: vectorofdouble; 

  private
    procedure Create();
    function func1(etc): integer;
  public
    procedure ReadFile(const FileName, inputs: string);
  end;

implementation
procedure T_xyz.ReadFile();
////////
Read(F,np)
  //SetLength(vectorofdouble, np) // DOES NOT WORK
  for i := 0 to maxval // I DONT WANT TO LOOP UP TO MAXVAL
  begin
    var1[i] := 0
  end;

procedure T_xyz.func1(etc);
////////
do stuff
  for i := 0 to maxval // I DONT WANT TO LOOP UP TO MAXVAL
  begin
    var2[i] := 0
  end;
end;

end.

@Brian as soon as i change from vectorofdouble = [1...maxval] of double; to vectorofdouble= array of double; i can not really access to vectorofdouble any where in the code setlength gives error — user2375049
– user2375049, Commented Jan 30, 2020 at 13:48
You need to pass the array rather than the type to SetLength. So, for instance, SetLength(var1, ...). By the way, what does OFlex stand for? — David Heffernan
– David Heffernan, Commented Jan 30, 2020 at 14:00
Delphi 10.3 Rio. If I use "vectorofdouble= array of double;" under the type (see above) and f.e add a SetLength(vectorofdouble,10); in any function [dcc32 Error] filename.pas(438): E2029 '(' expected but ',' found — user2375049
– user2375049, Commented Jan 30, 2020 at 14:02
@DavidHeffernan it is the main code i deal with the example above is just a dummy. SetLength(var1, ...) works fine however i have 30 variables that "inherit" from vectorofdouble var1, var2 varxxx. The code above allows it to be allocated once instead of for each variable is there a method — user2375049
– user2375049, Commented Jan 30, 2020 at 14:05

Remy Lebeau · Accepted Answer · 2020-01-30 16:25:39Z

3

You want to use a dynamic array instead of a fixed-length array. You do that by using

array of <Type>

instead of

array[<Low>..<High>] of <Type>

Then SetLength() will work, but you need to pass it a dynamic array variable instead of a type.

Try this:

unit xyz;

interface

uses
  abc;

type
  vectorofdouble = array of double;

type
  T_xyz = object
  public
    NP: integer;
  private
    var1: vectorofdouble;
    var2: vectorofdouble;
  public
    number: integer;
    var3: vectorofdouble;
  private
    procedure Create();
    function func1(etc): integer;
  public
    procedure ReadFile(const FileName, inputs: string);
  end;

implementation

procedure T_xyz.ReadFile();
var
  i: integer;
begin
  Read(F, NP);
  SetLength(var1, NP);
  for i := 0 to NP-1 do
  begin
    var1[i] := 0;
  end;
end;

procedure T_xyz.func1(etc);
begin
  for i := Low(var2) to High(var2) do
  begin
    var2[i] := 0;
  end;
end;

end.

edited Jan 30, 2020 at 16:25

answered Jan 30, 2020 at 16:20

Remy Lebeau

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1 Comment

user2375049 Over a year ago

i am not sure to answer this answer because : var2 is missing a setlength(var2,Np) argument which can be misleading as if it is enough to allocate var1 only.

David Heffernan · Accepted Answer · 2020-01-30 15:05:53Z

-1

You must pass the array to SetLength rather than the type. So instead of

SetLength(vectorofdouble, np)

you must use

SetLength(var1, np)

answered Jan 30, 2020 at 15:05

David Heffernan

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