Title: Delphi Implementation of C# StringBuilder (Fast String Concat)
Question: Those of you who use C# know that to concatenate a large number of strings takes forever unless you use the StringBulder class. This is a Delphi implementation of such and huge increase in performance can be gained by using it. On my machine the following timings were experienced.
procedure TForm1.Button1Click(Sender: TObject);
var oBuilder : TStringBuilder;
sString : string;
i,iCount : integer;
begin
iCount := 10000;
oBuilder := TStringBuilder.Create;
for i := 1 to iCount do oBuilder.Append(IntToStr(i));
sString := oBuilder.AsString;
// 6 Milliseconds
sString := '';
for i := 1 to iCount do sString := sString + IntToStr(i);
// 404 Milliseconds
FreeAndNil(oBuilder);
end;
As can be seen by the above the difference is dramatic as the normal Delphi concatenation must constantly increase and move the string memory around. One might be tempted to use a TStringList.Add(string) and then use the TStringList.Text property, but the Carriage Return and Line Feed pairs appear in the Text.
Answer:
unit MahStringBuilder;
interface
// ==========================================================================
// Implementation of C# StringBuilder class.
// Mike Heydon 2008
//
// Allow fast string concatenation without excessive memory rellocs.
// Default Initial Buffer Size is 4K and doubles for each reallocation, but
// can be set to a higher or lower value for performance if the size of
// the resulting string is predicatble.
//
// Example
//
// procedure TForm1.Button1Click(Sender: TObject);
// var oString : TStringBuilder;
// i : integer;
// begin
// oString := TStringBuilder.Create;
// for i := 1 to 100 do oString.Append(IntToStr(i) + ' ');
// oString.Append('100 Numbers ');
// Memo1.Lines.Add(oString.AsString);
// oString.Append('Some More ExtraText');
// Memo1.Lines.Add(oString.AsString);
// FreeAndNil(oString);
// end;
//
// ==========================================================================
type
{ TStringBuilder Class }
TStringBuilder = class(TObject)
private
FBuffMax,
FBuffSize,FIndex : integer;
FBuffer : PChar;
procedure _ExpandBuffer;
function GetFString : string;
procedure SetFString(const AString : string);
public
constructor Create(ABufferSize : integer = 4096);
destructor Destroy; override;
procedure Append(const AString : string);
procedure Clear;
property AsString : string read GetFString write SetFString;
end;
// --------------------------------------------------------------------------
implementation
procedure TStringBuilder._ExpandBuffer;
begin
FBuffSize := FBuffSize shl 1;
FBuffMax := FBuffSize - 1;
ReallocMem(FBuffer,FBuffSize);
end;
constructor TStringBuilder.Create(ABufferSize : integer = 4096);
begin
inherited Create;
if ABufferSize FBuffSize := 1024
else
FBuffSize := ABufferSize;
GetMem(FBuffer,FBuffSize);
FBuffMax := FBuffSize - 1;
FIndex := 0;
end;
destructor TStringBuilder.Destroy;
begin
FreeMem(FBuffer);
inherited Destroy;
end;
procedure TStringBuilder.Append(const AString : string);
var iLen : integer;
begin
iLen := length(AString);
if iLen + FIndex FBuffMax then _ExpandBuffer;
move(AString[1],FBuffer[FIndex],iLen);
inc(FIndex,iLen);
end;
function TStringBuilder.GetFString : string;
begin
FBuffer[FIndex] := #0;
Result := FBuffer;
end;
procedure TStringBuilder.SetFString(const AString : string);
begin
self.Clear;
self.Append(AString);
end;
procedure TStringBuilder.Clear;
begin
FIndex := 0;
end;
end.