ストリーム(IStream)の確実なサイズの取得

    static DWORD GetStreamSize(IStreamPtr spStream)

    {

        if (spStream == NULL)

        {

            ATLASSERT(0);

            return 0;

        }

        HRESULT hr = S_OK;

        hr = CStreamHelper::RewindSeekPosition(spStream);

        if (FAILED(hr))

        {

            ATLASSERT(0);

            return 0;

        }

#if 0    // この方法ではXMLDOMからサイズが取れない

        // サイズの取得

        LARGE_INTEGER zeroPos = {0, 0};

        ULARGE_INTEGER StreamSize = {0, 0};

        hr = spStream->Seek(zeroPos, STREAM_SEEK_END, &StreamSize);

        if (FAILED(hr))

        {

            ATLASSERT(0);

            return 0;

        }

        return (DWORD)StreamSize.QuadPart;

#else

        DWORD dwSize = 0;

        for (dwSize = 0; ; dwSize++)

        {

            BYTE cTemp;

            ULONG ulRead = 0;

            hr = spStream->Read(&cTemp, 1, &ulRead);

            if (hr != S_OK || ulRead == 0)

            {

                break;

            }

        }

        return dwSize;

#endif

    }

    // シーク位置を先頭に戻す

    static HRESULT RewindSeekPosition(IStreamPtr spStream)

    {

        if (spStream == NULL)

        {

            ATLASSERT(0);

            return E_FAIL;

        }

        HRESULT hr = S_OK;

        // 先頭に戻す

        LARGE_INTEGER zeroPos = {0, 0};

        ULARGE_INTEGER StreamSize = {0, 0};

        hr = spStream->Seek(zeroPos, STREAM_SEEK_SET, &StreamSize);

        if (FAILED(hr))

        {

            ATLASSERT(0);

            return hr;

        }

        return hr;

    }