LARGE_INTEGER or TLargeInteger?

Question

In Windows.pas, there are:

  LARGE_INTEGER = record
    case Integer of
    0: (
      LowPart: DWORD;
      HighPart: Longint);
    1: (
      QuadPart: LONGLONG);
  end;

  TLargeInteger = Int64;

I see several Windows functions and structure members which is originally declared as LARGE_INTEGER has been translated to TLargeInteger such as:

  function QueryPerformanceCounter(var lpPerformanceCount: TLargeInteger): BOOL;
      stdcall;

and another example is:

  WIN32_STREAM_ID = record
    dwStreamId        : DWORD;
    dwStreamAttributes: DWORD;
    Size              : TLargeInteger;
    dwStreamNameSize  : DWORD;
    cStreamName       : array[0..0] of WCHAR;
  end;

Can TLargeInteger acts as a replacement of LARGE_INTEGER for every function parameters and structure members found in Windows header files?

Answer 1

You can always safely use these two types interchangeably in API translations. Although, clearly, once you have selected one type for a particular function, you have to stick to that type whenever you call that function.

• Using TLargeInteger makes it easier to assign values because there's no need to refer to a record field.
• Using LARGE_INTEGER makes it easier to separate into low and high 32 bit parts.

Now that the compiler has good support for 64 bit integers, it probably makes more sense to use TLargeInteger. Because, usually, there is no need to separate the 64 bit integer into its low and high parts. But way back when the compiler couldn't handle 64 bit integer types, there was no other option to work with 64 bit integers.