Direct3D 9 functions return value

Question

Since the function's return value is utilized for error message, how do the functions return the necessary information back to the caller?

For example: IDirect3D9::CreateDevice method

Answer 1

So if you take a look at that link you'll notice that it has some parameters marked Out this is important because this denotes what will be returned to the caller.

HRESULT CreateDevice(
[in]           UINT Adapter,
[in]           D3DDEVTYPE DeviceType,
[in]           HWND hFocusWindow,
[in]           DWORD BehaviorFlags,
[in, out]      D3DPRESENT_PARAMETERS *pPresentationParameters,
[out, retval]  IDirect3DDevice9 **ppReturnedDeviceInterface
);

In the above sample (copied and pasted from the MSDN link), you'll notice a parameter ppReturnedDeviceInterface is marked as being ** or a pointer to a pointer, the caller would pass in a the address of their pointer and would be returned a pointer at that address. Also the D3DPRESENT_PARAMETERS structure passed in to pPresentationParameters will be updated on return, as noted by the out annotation. Ex:

IDirect3DDevice9 *pDevice = NULL;

HRESULT hr = pD3D->CreateDevice(
                     D3DADAPTER_DEFAULT,
                     D3DDEVTYPE_HAL,
                     hwnd,
                     pPresentationParams,
                     &pDevice);
 if(SUCCEEDED(hr))
 {
    //pDevice should be non null at this point
 }