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

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?

Solution

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