DWORD_PTR, INT_PTR, LONG_PTR, UINT_PTR, ULONG_PTR When, How and Why?

windows winapi mfc
ju. picture ju. · Aug 13, 2009 · Viewed 22.9k times · Source

I found that Windows has some new Windows Data Types

DWORD_PTR, INT_PTR, LONG_PTR, UINT_PTR, ULONG_PTR

can you tell me when, how and why to use them?

Answer

Chris Becke picture Chris Becke · Aug 13, 2009

The *_PTR types were added to the Windows API in order to support Win64's 64bit addressing.

Because 32bit APIs typically passed pointers using data types like DWORD, it was necessary to create new types for 64 bit compatibility that could substitute for DWORD in 32bit applications, but were extended to 64bits when used in a 64bit applications.

So, for example, application developers who want to write code that works as 32bit OR 64bit the windows 32bit API SetWindowLong(HWND,int,LONG) was changed to SetWindowLongPtr(HWND,int,LONG_PTR)

In a 32bit build, SetWindowLongPtr is simply a macro that resolves to SetWindowLong, and LONG_PTR is likewise a macro that resolves to LONG. In a 64bit build on the other hand, SetWindowLongPtr is an API that accepts a 64bit long as its 3rd parameter, and ULONG_PTR is typedef for unsigned __int64.

By using these _PTR types, one codebase can compile for both Win32 and Win64 targets.

When performing pointer arithmetic, these types should also be used in 32bit code that needs to be compatible with 64bit.

so, if you need to access an array with more than 4billion elements, you would need to use an INT_PTR rather than an INT

  CHAR* pHuge = new CHAR[0x200000000]; // allocate 8 billion bytes
  INT idx;
  INT_PTR idx2;
  pHuge[idx]; // can only access the 1st 4 billion elements.
  pHuge[idx2]; // can access all 64bits of potential array space.

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