What do [in] and [out] mean in MSDN method documention?

Question

In http://msdn.microsoft.com/en-us/library/vstudio/ms164519(v=vs.100).aspx, there is

HRESULT VirtualProtect (
    [in]  void*   lpAddress,
    [in]  SIZE_T  dwSize,
    [in]  DWORD   flNewProtect,
    [out] DWORD*  pflOldProtect
);

What do the [in] and [out] mean?

Answer 1

That's showing which parameters are "inputs" and which are "outputs". In this case, the address, size, and newProtect flags are all read in, and pflOldProtect is written to as an output.

Answer 2

[in] means that the parameter is used by the function; [out] means that the parameter is returned by the function.