ole_query_interface

static VALUE
fole_query_interface(VALUE self, VALUE str_iid)
{
    HRESULT hr;
    OLECHAR *pBuf;
    IID iid;
    struct oledata *pole = NULL;
    IDispatch *pDispatch;
    void *p;

    pBuf  = ole_vstr2wc(str_iid);
    hr = CLSIDFromString(pBuf, &iid);
    SysFreeString(pBuf);
    if(FAILED(hr)) {
        ole_raise(hr, eWIN32OLERuntimeError,
                  "invalid iid: `%s'",
                  StringValuePtr(str_iid));
    }

    pole = oledata_get_struct(self);
    if(!pole->pDispatch) {
        rb_raise(rb_eRuntimeError, "failed to get dispatch interface");
    }

    hr = pole->pDispatch->lpVtbl->QueryInterface(pole->pDispatch, &iid,
                                                 &p);
    if(FAILED(hr)) {
        ole_raise(hr, eWIN32OLEQueryInterfaceError,
                  "failed to get interface `%s'",
                  StringValuePtr(str_iid));
    }

    pDispatch = p;
    return create_win32ole_object(cWIN32OLE, pDispatch, 0, 0);
}