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I want to P/Invoke to GetWindowLongPtr and SetWindowLongPtr , and I'm seeing conflicting information about them. Some sources say that, on 32-bit platforms, GetWindowLongPtr is just a preprocessor macro that calls GetWindowLong, and GetWindowLongPtr doesn't exist as an entry point in user32.dll. For example: The pinvoke.net entry for SetWindowLongPtr has a static method that checks IntPtr.Size and then calls either SetWindowLong or SetWindowLongPtr, with a comment saying that "legacy OSes do not support SetWindowLongPtr". There's no explanation of what is meant by "legacy OSes". An answer on StackOverflow states "On 32bit systems GetWindowLongPtr is just a C macro that points to GetWindowLong". So these sources seem to indicate that the *Ptr entry points simply aren't there in the version of user32.dll that ships with, say, 32-bit Windows 7. But I see no indication of this in the MSDN documentation. According to MSDN, SetWindowLongPtr supersedes SetWindowLong, plain and simple. And according to the requirements section of the SetWindowLongPtr page , it appears that SetWindowLongPtr has been in user32.dll since Windows 2000 (both client and server editions). Again, no mention of the entry points being missing in 32-bit OSes. I suspect that the truth is somewhere in between: that when you tell the C++ compiler to target older OSes (i.

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