Strings and high memory usage

Question

When I run this code in XE4, the application ends up using ~800 MB.

Why not closer to 100 MB ?

Using Ansistring instead of string makes no difference.

const
  N = 10000000; // 10 million
  M = 10;
var
  i,j: integer;
  s: string;
  X: array of string;
begin
  setlength(X,N);
  for i:= 1 to N do
  begin
    s:= '';
    for j:= 1 to M do s:= s+chr(65+random(25));
    X[i-1]:= s;
  end;
  showmessage('pause');
end;

Answer 1

A string of length 10 in XE4 uses 34 Bytes of memory (see DocWiki). 20 Bytes for the content, 2 Bytes for the #0 terminator and 12 bytes management data.

Each array entry is a pointer to that kind of memory. Thus those 10 million strings in the array end up using 380 MB (340 for the strings and 40 for the array items) of memory at minimum.

Answer 2

Try this

const MaxString = 15; // you said so

type stringholder = record
  strict private 
     var Cell: string[ MaxString * SizeOf(Char) div SizeOf(AnsiChar) ];
     function GetUS: String; // in xe 4 that is a shortcut to UnicodeString actual type
     procedure SetUS(const US: string); 
  public
     property Value: string read GetUS write SetUS;
     class operator Implicit(const from: string): stringholder; inline;
     class operator Implicit(const from: stringholder): string; inline;
  end;

function stringholder.GetUS: String;
var i: integer;
begin
  i := Ord( Cell[0] );
  SetLength( Result, i div (SizeOf(Char) div SizeOf(AnsiChar)) );
  if i > 0 then
     Move( Cell[1], Result[1], i);
end;

procedure SetUS(const US: string);
var i: integer;
begin
  If US = '' then begin
     Cell := ''; // constant here, not US itself
     Exit;
  End;

  i := Length(US);
  If i > MaxString then raise EInvalidCast.Create('.....'+US);

  i := i * SizeOf(Char) div SizeOf(AnsiChar)
  Move( US[1], Cell[1], i );
  Cell(. 0 .) := AnsiChar(i);
end;

class operator stringholder.Implicit(const from: string): stringholder;
begin
  Result.Value := from;
end;

class operator stringholder.Implicit(const from: stringholder): string;
begin
  Result := from.Value;
end;


const
  N = 10000000; // 10 million
  M = 10;
var
  i,j: integer;
  s: string;
  X: array of stringholder;
begin
  setlength(X,N);
  for i:= 1 to N do
  begin
    s:= '';
    for j:= 1 to M do s:= s+chr(65+random(25));
    X(. i-1 .) := s;
  end;
  showmessage('pause');
end;