C++模板会使代码膨胀吗

今天和同事说到C++模板会使代码膨胀, 可同事觉得不会。
同事的依据是: 如果模板会使代码膨胀, 那么ATL和WTL里为什么还要大量使用模板? 同样功能，ATL和WTL编译出的可执行文件可比MFC编译的要小的多。
我当时一愣，事实确实如同事所说，难道模板会使代码膨胀的观点是错误的吗?

MFC因为本身代码量和复杂性在那里，所以它生成比较大的exe无可厚非。我们这里重点关注为什么ATL/WTL使用模板，但是却不会使生成的exe变大。www.zzzyk.com

我们知道使用模板时，同一模板生成不同的模板实类后会是多份代码，比如 vector<int>， vector<char>, vector<double>, 这里总共会生成3份不同的vector代码，这就是我们平时所说的代码膨胀。

那么为什么ATL/WTL就没有代码膨胀的问题呢?
我这里以 ATL里的窗口代码为例来分析这个问题，因为我对WinDbg比较熟悉，下面我会以WinDbg为工具来分析我以前的写得那个俄罗斯方块程序。

首先我们看一下ATL的窗口代码:
template <class T, class TBase /* = CWindow */, class TWinTraits /* = CControlWinTraits */>
class ATL_NO_VTABLE CWindowImpl : public CWindowImplBaseT< TBase, TWinTraits >
{
public:
DECLARE_WND_CLASS(NULL)

    static LPCTSTR GetWndCaption()
    {
        return NULL;
    }

    HWND Create(HWND hWndParent, _U_RECT rect = NULL, LPCTSTR szWindowName = NULL,
            DWORD dwStyle = 0, DWORD dwExStyle = 0,
            _U_MENUorID MenuOrID = 0U, LPVOID lpCreateParam = NULL)
    {
        if (T::GetWndClassInfo().m_lpszOrigName == NULL)
            T::GetWndClassInfo().m_lpszOrigName = GetWndClassName();
        ATOM atom = T::GetWndClassInfo().Register(&m_pfnSuperWindowProc);

dwStyle = T::GetWndStyle(dwStyle);
dwExStyle = T::GetWndExStyle(dwExStyle);

        // set caption
        if (szWindowName == NULL)
            szWindowName = T::GetWndCaption();

        return CWindowImplBaseT< TBase, TWinTraits >::Create(hWndParent, rect, szWindowName,
            dwStyle, dwExStyle, MenuOrID, atom, lpCreateParam);
    }
};
上面是一个模板类，它应该会生成多份模板实例代码：我们可以用WinDbg的符号搜索命令来做验证:
输入 x HYTeris!ATL::CWindowImpl<* ，搜索所有以 HYTeris!ATL::CWindowImpl< 开头的符号
0:000> x HYTeris!ATL::CWindowImpl<*
004592f0 HYTeris!ATL::CWindowImpl<CTsButton,WTL::CButtonT<ATL::CWindow>,ATL::CWinTraits<1442840576,0> >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
004343a0 HYTeris!ATL::CWindowImpl<CTsMainStatusPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::~CWindowImpl<CTsMainStatusPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> > (void)
00437c90 HYTeris!ATL::CWindowImpl<CTsMainControlPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::GetWndCaption (void)
00430440 HYTeris!ATL::CWindowImpl<CTsGameMainWnd,ATL::CWindow,ATL::CWinTraits<114229248,262400> >::CWindowImpl<CTsGameMainWnd,ATL::CWindow,ATL::CWinTraits<114229248,262400> > (void)
0041c990 HYTeris!ATL::CWindowImpl<CTsAgentWindow,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::GetWndCaption (void)
0044cf50 HYTeris!ATL::CWindowImpl<CTsNextElementContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::~CWindowImpl<CTsNextElementContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> > (void)
004539a0 HYTeris!ATL::CWindowImpl<CTsMutiScoreContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
00435800 HYTeris!ATL::CWindowImpl<CTsGameMainWnd,ATL::CWindow,ATL::CWinTraits<114229248,262400> >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
00434640 HYTeris!ATL::CWindowImpl<CTsKeyEdit,WTL::CEditT<ATL::CWindow>,ATL::CWinTraits<1442840576,0> >::~CWindowImpl<CTsKeyEdit,WTL::CEditT<ATL::CWindow>,ATL::CWinTraits<1442840576,0> > (void)
00437440 HYTeris!ATL::CWindowImpl<CTsGameMainWnd,ATL::CWindow,ATL::CWinTraits<114229248,262400> >::GetWndCaption (void)
00436020 HYTeris!ATL::CWindowImpl<CTsMainButtonPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
00453f70 HYTeris!ATL::CWindowImpl<CTsNextElementContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::GetWndCaption (void)
00424e30 HYTeris!ATL::CWindowImpl<CTsDisplayContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::~CWindowImpl<CTsDisplayContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> > (void)
004338a0 HYTeris!ATL::CWindowImpl<CTsMainButtonPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::~CWindowImpl<CTsMainButtonPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> > (void)
0041c4f0 HYTeris!ATL::CWindowImpl<CTsAgentWindow,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
00441b50 HYTeris!ATL::CWindowImpl<CTsKeyEdit,WTL::CEditT<ATL::CWindow>,ATL::CWinTraits<1442840576,0> >::CWindowImpl<CTsKeyEdit,WTL::CEditT<ATL::CWindow>,ATL::CWinTraits<1442840576,0> > (void)
004365f0 HYTeris!ATL::CWindowImpl<CTsMainControlPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
00455120 HYTeris!ATL::CWindowImpl<CTsButton,WTL::CButtonT<ATL::CWindow>,ATL::CWinTraits<1442840576,0> >::CWindowImpl<CTsButton,WTL::CButtonT<ATL::CWindow>,ATL::CWinTraits<1442840576,0> > (void)
0040ea20 HYTeris!ATL::CWindowImpl<CTsDisplayContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
00453fa0 HYTeris!ATL::CWindowImpl<CTsSingleScoreContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::GetWndCaption (void)
0041abc0 HYTeris!ATL::CWindowImpl<CTsAgentWindow,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::CWindowImpl<CTsAgentWindow,ATL::CWindow,ATL::CWinTraits<1442840576,0> > (void)
00459c20 HYTeris!ATL::CWindowImpl<CTsSubControlContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::CWindowImpl<CTsSubControlContainer,ATL::CWindow,ATL::CWinTraits<1442840576,0> > (void)
0045f640 HYTeris!ATL::CWindowImpl<CTsUserListCtrl,WTL::CListViewCtrlT<ATL::CWindow>,ATL::CWinTraitsOR<32777,0,ATL::CWinTraits<1442840576,0> > >::Create (struct HWND__ *, class ATL::_U_RECT, wchar_t *, unsigned long, unsigned long, class ATL::_U_MENUorID, void *)
004608a0 HYTeris!ATL::CWindowImpl<CTsSingleControlPane,ATL::CWindow,ATL::CWinTraits<1442840576,0> >::GetWndClassInfo (void)
0045fed0 HYTeris!ATL::CWindowIm

补充：软件开发 , C++ ,