create_guid

static VALUE
fole_s_create_guid(VALUE self)
{
    GUID guid;
    HRESULT hr;
    OLECHAR bstr[80];
    int len = 0;
    hr = CoCreateGuid(&guid);
    if (FAILED(hr)) {
        ole_raise(hr, eWIN32OLERuntimeError, "failed to create GUID");
    }
    len = StringFromGUID2(&guid, bstr, sizeof(bstr)/sizeof(OLECHAR));
    if (len == 0) {
        rb_raise(rb_eRuntimeError, "failed to create GUID(buffer over)");
    }
    return ole_wc2vstr(bstr, FALSE);
}