[NumLock]

подытожим:

Buffer: array [0..$ff] of Char

Код:

var
  hFile: THandle;
  Buffer: array [0..$ff] of Char;
  Dummy: DWORD;
begin
  hFile:=CreateFile('Unit1.pas', GENERIC_READ, 0, nil, OPEN_EXISTING, 0, 0);
  ReadFile(hFile,
    Buffer[0],
    $100,
    Dummy, nil); 
  ShowMessage(Copy(Buffer, 1, Dummy));
  CloseHandle(hFile);
end;

Buffer: array of Char

Код:

var
  hFile: THandle;
  Buffer: array of Char;
  Dummy: DWORD;
begin
  SetLength(Buffer, $100);
  hFile:=CreateFile('Unit1.pas', GENERIC_READ, 0, nil, OPEN_EXISTING, 0, 0);
  ReadFile(hFile,
    Buffer[0],
    $100,
    Dummy, nil); 
  ShowMessage(Copy(String(@Buffer[0]), 1, Dummy));
  CloseHandle(hFile);
end;

Buffer: Pointer

Код:

var
  hFile: THandle;
  Buffer: Pointer; 
  Dummy: DWORD;
begin
  Buffer:=GetMemory($100);
  hFile:=CreateFile('Unit1.pas', GENERIC_READ, 0, nil, OPEN_EXISTING, 0, 0);
  ReadFile(hFile,
    Buffer^,
    $100,
    Dummy, nil); 
  ShowMessage(Copy(PChar(Buffer), 1, Dummy));
  CloseHandle(hFile);
  FreeMemory(Buffer);
end;

Buffer: String

Код:

var
  hFile: THandle;
  Buffer: String;
  Dummy: DWORD;
begin
  SetLength(Buffer, $100);
  hFile:=CreateFile('Unit1.pas', GENERIC_READ, 0, nil, OPEN_EXISTING, 0, 0);
  ReadFile(hFile,
    PChar(@Buffer[1])^,
    $100,
    Dummy, nil);
  ShowMessage(Copy(Buffer, 1, Dummy));
  CloseHandle(hFile);
end;