syscall-如何在Go中使用LPWSTR？

Question

I'm trying to create a thin wrapper of Windows MMDevice API for Go, and I faced the problem about Windows data types for strings. According to the documentation of IMMDevice::GetId method, it takes the parameter below:

HRESULT GetId(
    [out] LPWSTR *ppstrId
);

And here is my Go code that corresponds to the method above. (github.com/moutend/ywca/immdevice_windows.go:13)

func getId(mmd *IMMDevice, strId *uint16) (err error) {
    hr, _, _ := syscall.Syscall(
        mmd.VTable().GetId,
        2,
        uintptr(unsafe.Pointer(mmd)),
        uintptr(unsafe.Pointer(strId)),
        0)
    // ...
}

My understand is that the LPWSTR is the pointer to the array of uint16 values, but it causes invalid pointer error. What type should I use in this case? Thanks.

Answer 1

It is a pointer to a pointer. The LPWSTR type is a wchar_t* and therefor the parameter in that method is a wchar_t**.

You are not passing in a string buffer for the method to fill. The method will allocate memory with CoTaskMemAlloc and return this memory address back to you after it has been filled. You are responsible for freeing this memory with CoTaskMemAlloc.