C++ 使用 toString 模板和列表对象 - 多态性

Question

我是c++的新程序员，我有一个任务是编写一个多态任务。程序中有一个toString模板，我不允许编辑。

我有一个<< operator in which I call an overloaded method with each class, the print itself for example cout << and it works correctly, but if I want to use the toString method for the same thing, it only works sometimes. You don't know where I'm doing wrong. I am attaching the entire program: https://godbolt.org/z/e8rrqTsEY

PS：我没有选择架构（我的意思是有一些断言等）所以添加方法和其他一些方法就是这样

class CWindow
{
  public:
    ...
    CWindow& add(const CWindow &x);
    virtual unique_ptr<CWindow> createInstance() const;
    unique_ptr<CWindow> &search(int id);
    ...

    virtual void printData(ostream &os, bool last) const;
    friend ostream& operator << (ostream &os, const CWindow &src);

  protected:
    static multimap<int,unique_ptr<CWindow>> m_Db; 
   ..
};

unique_ptr<CWindow> CWindow::createInstance() const
{
    return make_unique<CWindow>(*this);
}

CWindow &CWindow::add(const CWindow &x)
{
  unique_ptr<CWindow> ptr = x.createInstance();
  ..
  m_Db.emplace(ptr->m_Id, move(ptr));
  return *this;
}

unique_ptr<CWindow>& CWindow::search(int id) {
  auto it = m_Db.find(id);

  if (it != m_Db.end())
    return it->second;
  
  
  static unique_ptr<CWindow> null_ptr = nullptr;
  return null_ptr;
}

void CWindow::printData(ostream &os, bool last) const
{
  os << "[" << m_Id  << "] Window " << "\"" << m_Title << "\" " << "(" <<  m_AbsPos.m_X << "," << m_AbsPos.m_Y << "," << m_AbsPos.m_W << "," << m_AbsPos.m_H << ")" << "\n";

    bool lastt = false;
    size_t index = 0;

    for(const auto &x : m_Db)
    {
      lastt = index++ == (m_Db.size() -1 );
      x.second->printData(os, lastt);
    }
}


ostream& operator << (ostream &os, const CWindow &src)
{
    src.printData(os, false);
    return os;
}

class CButton : public CWindow
{
  public:
    ..
    virtual unique_ptr<CWindow> createInstance() const;
    virtual void printData(ostream &os, bool last) const override;
    
};

void CButton::printData(ostream &os, bool last) const
{
  os << "+- [" << m_Id << "] Button " << "\"" << m_Title << "\" (" << m_AbsPos.m_X << "," << m_AbsPos.m_Y << "," << m_AbsPos.m_W << "," << m_AbsPos.m_H << ")" << "\n"; 
}

unique_ptr<CWindow> CButton::createInstance() const
{
  return make_unique<CButton>(*this);
}

template <typename _T>
string toString ( const _T & x )
{
  ostringstream oss;
  oss << x;
  return oss . str ();
}

int main()
{
  cout << "work:" << endl;
  cout << *a . search ( 20 );
  cout << "work:" << endl;
  cout << toString(a);
  cout << "not work" << endl;
  toString ( *b . search ( 20 ) );

其他类还有CInput、CLabel和CComboBox，但它们的工作原理与CButton基本相同，所以这里省略。提前感谢所有评论

C++ 使用 toString 模板和列表对象 - 多态性