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var
  Form1: TForm1;
  sCont: PChar;
  pCont: ^Char;
  nSize: Integer;

implementation

{$R *.dfm}

Function MyReplace(sBuffer: PChar; sSource: PChar; sSearch: PChar; sReplace: PChar): PChar; StdCall; external 'replaceDLL.dll' name 'strReplace';

procedure TForm1.Button1Click(Sender: TObject);
begin
sCont := PChar(RichEdit1.Text);
nSize := StrLen(sCont);
GetMem(pCont, nSize);
RichEdit1.Text := MyReplace(pCont,
                            sCont,
                            '1',
                            '2');
end;					

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procedure TForm1.ButtonReplaceClick(Sender: TObject);

var
  pSource: PChar;
  pSearch: PChar;
  pReplace: PChar;
  pResult: PChar;
  nSource: Integer;
  nSearch: Integer;
  nReplace: Integer;
  nResult: Integer;

begin
  pSource := PChar(RichEditSource.Text);
  pSearch := PChar(RichEditSearch.Text);
  pReplace := PChar(RichEditReplace.Text);
  ;
  nSource := StrLen(pSource);
  nSearch := StrLen(pSearch);
  nReplace := StrLen(pReplace);
  ;
  if(nSearch > 0) then
  begin
    nResult := (nSource div nSearch)* nReplace + nSource mod nSearch;
    if(nResult < nSource) then nResult := nSource;
    GetMem(pResult, nResult + 1);
    MyReplace(pResult, pSource, pSearch, pReplace);
    RichEditSource.Text := AnsiString(pResult);
    FreeMem(pResult);
  end;
end;					

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procedure DelphiStrReplace(sBuff: PChar; sCont: PChar; sSearch: PChar; sRepl: PChar);
var
  nToCopy: Integer;
  pCont: PChar;
  pSearch: PChar;

begin
  if not (sSearch^ = '\0') then
  begin
    sBuff := sCont;
  end
  else
  begin
    //sBuff^ := '\0';//hier gibt es Troubles
    nToCopy := 0;
    while not (sCont^ = '\0') do
    begin
      if(sCont^ = sSearch^) then
      begin
        pCont := sCont;
        pSearch := sSearch;
        while(((++pCont)^ = (++pSearch)^) and (pCont^) and (pSearch^));//hier auch
        ;
        if(pSearch^ = '\0') then             //soweit ist der Compiler noch nicht gekommen
        begin
          strncat(sBuff, (sCont - nToCopy), nToCopy);
          nToCopy := 0;
          strcat(sBuff, sRepl);
          sCont += nSearch;
          continue;
        end;
      end;
      sCont++;
      nToCopy++;
    end;
    strncat(sBuff, (sCont - nToCopy), nToCopy);
  end;
end;					

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p := PChar( 'ABC');
inc(p);
=> p := 'BC';					

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procedure DelphiStrReplace(sBuff: PChar; sCont: PChar; sSearch: PChar; sRepl: PChar);

var
  pCont: PChar;
  pSearch: PChar;
  nToCopy: Integer;
  nSearch: Integer;

begin
  if (sSearch^ = #0) then
  begin
    sBuff := sCont;
  end
  else
  begin
    sBuff^ := #0;
    nToCopy := 0;
    nSearch := StrLen(sSearch);
    while not (sCont^ = #0) do
    begin
      if(sCont^ = sSearch^) then
      begin
        pCont := sCont;
        pSearch := sSearch;
        while( (pCont^ = pSearch^) and (not (pCont^ = #0)) and (not (pSearch^ = #0)) ) do
        begin
          inc(pCont);
          inc(pSearch);
        end;

        if(pSearch^ = #0) then
        begin
          StrLCat(sBuff, (sCont - nToCopy), (StrLen(sBuff) + nToCopy));
          nToCopy := 0;
          StrCat(sBuff, sRepl);
          sCont := sCont + nSearch;
          continue;
        end;
      end;
      inc(sCont);
      inc(nToCopy);
    end;
    StrLCat(sBuff, (sCont - nToCopy), (StrLen(sBuff) + nToCopy));
  end;
end;					

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procedure MyStringPaste(nBuff: Integer; sBuff: PChar; sToPaste: PChar; nToPaste: Integer);

var
  nIndex: Integer;
  nCount: Integer;
  nLastPos: Integer;

begin
  nCount := 0;
  nLastPos := nBuff + nToPaste - 1;
  for nIndex := nBuff to nLastPos do
  begin
    sBuff[nIndex] := sToPaste[nCount];
    inc(nCount);
  end;
  sBuff[nIndex ] := #0;

end;