declare_dyncreate_waxgourd0的专栏

你是否正在寻找关于declare_dyncreate的内容？让我把最俱价值的东西奉献给你：

随便搜索一下，发现给出的解释是在运行期让派生类支持动态创建，可是给出详细解释的却很少，那么下面仔细看看此宏的扩展：

#define DECLARE_DYNCREATE(class_name) \ DECLARE_DYNAMIC(class_name) \ static CObject* PASCAL CreateObject(); #define _declare_dyncreate(class_name) \ _DECLARE_DYNAMIC(class_name) \ static CObject* PASCAL CreateObject();

从上面看到 declare_dyncreate 内部使用了 DECLARE_DYNAMIC 宏，那么设想一下是否 IMPLEMENT_DYNCREATE 内部也应该使用 IMPLEMENT_DYNAMIC宏，我们来看看是不是这样：

#define IMPLEMENT_DYNCREATE(class_name, base_class_name) \ CObject* PASCAL class_name::CreateObject() \ { return new class_name; } \ IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, 0xFFFF, \ class_name::CreateObject, NULL)
发现并没有IMPLEMENT_DYNAMIC 宏，别着急，让我们先来看看IMPLEMENT_DYNAMIC 宏：
#define IMPLEMENT_DYNAMIC(class_name, base_class_name) \ IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, 0xFFFF, NULL, NULL)

这样看来他们在内部是相同的，内部是使用 DECLARE_DYNAMIC 、IMPLEMENT_DYNAMIC，下面借来仔细观察这两个宏的内部拓展，。

IMPLEMENT_DYNAMIC 是实现“运行时类型识别”宏，与之相对应的是 DECLARE_DYNAMIC 声明“运行时类型识别”宏)。也就是说你在.CPP文件中如果看见有IMPLEMENT_DYNAMIC，则在.h文件中必定有DECLARE_DYNAMIC的声明。

DECLARE_DYNAMIC/DECLARE_DYNAMIC 是为了确定运行时对象属于哪一个类而定义的宏。

declare_dyncreate/IMPLEMENT_DYNCREATE 是为了“动态创建"类的实例而定义的宏。new可以用来创建对象，但不能在还不知道要创建那个类的对象时进行动态的创建。可以参考一个很普遍的例子：

char szClassName[60]; cin >> szClassName; CObject* pOb=new szClassName; //通不过
这里就要用到 declare_dyncreate/IMPLEMENT_DYNCREATE 定义的功能了。

查看afx.h头文件里的宏定义：

#ifdef _AFXDLL #define DECLARE_DYNAMIC(class_name) \ protected: \ static CRuntimeClass* PASCAL _GetBaseClass(); \ public: \ static const CRuntimeClass class##class_name; \ static CRuntimeClass* PASCAL GetThisClass(); \ virtual CRuntimeClass* GetRuntimeClass() const; \ #define _DECLARE_DYNAMIC(class_name) \ protected: \ static CRuntimeClass* PASCAL _GetBaseClass(); \ public: \ static CRuntimeClass class##class_name; \ static CRuntimeClass* PASCAL GetThisClass(); \ virtual CRuntimeClass* GetRuntimeClass() const; \ #else #define DECLARE_DYNAMIC(class_name) \ public: \ static const CRuntimeClass class##class_name; \ virtual CRuntimeClass* GetRuntimeClass() const; \ #define _DECLARE_DYNAMIC(class_name) \ public: \ static CRuntimeClass class##class_name; \ virtual CRuntimeClass* GetRuntimeClass() const; \ #endif

举例而言，如果你写DECLARE_DYNAMIC(CMyView)，则等于声明了一个静态变量

static CRuntimeClass classCMyView 然后是“virtual CRuntimeClass* GetRuntimeClass() const;”语句，其声明一个虚函数，函数名为GetRuntimeClass，返回为CRuntimeClass类型的指针，无形参，并且是个const函数。

#ifdef _AFXDLL #define IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, wSchema, pfnNew, class_init) \ CRuntimeClass* PASCAL class_name::_GetBaseClass() \ { return RUNTIME_CLASS(base_class_name); } \ AFX_COMDAT const CRuntimeClass class_name::class##class_name = { \ #class_name, sizeof(class class_name), wSchema, pfnNew, \ &class_name::_GetBaseClass, NULL, class_init }; \ CRuntimeClass* PASCAL class_name::GetThisClass() \ { return _RUNTIME_CLASS(class_name); } \ CRuntimeClass* class_name::GetRuntimeClass() const \ { return _RUNTIME_CLASS(class_name); } #define _IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, wSchema, pfnNew, class_init) \ CRuntimeClass* PASCAL class_name::_GetBaseClass() \ { return RUNTIME_CLASS(base_class_name); } \ AFX_COMDAT CRuntimeClass class_name::class##class_name = { \ #class_name, sizeof(class class_name), wSchema, pfnNew, \ &class_name::_GetBaseClass, NULL, class_init }; \ CRuntimeClass* PASCAL class_name::GetThisClass() \ { return _RUNTIME_CLASS(class_name); } \ CRuntimeClass* class_name::GetRuntimeClass() const \ { return _RUNTIME_CLASS(class_name); } #else #define IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, wSchema, pfnNew, class_init) \ AFX_COMDAT const CRuntimeClass class_name::class##class_name = { \ #class_name, sizeof(class class_name), wSchema, pfnNew, \ RUNTIME_CLASS(base_class_name), NULL, class_init }; \ CRuntimeClass* class_name::GetRuntimeClass() const \ { return RUNTIME_CLASS(class_name); } #define _IMPLEMENT_RUNTIMECLASS(class_name, base_class_name, wSchema, pfnNew, class_init) \ AFX_COMDAT CRuntimeClass class_name::class##class_name = { \ #class_name, sizeof(class class_name), wSchema, pfnNew, \ RUNTIME_CLASS(base_class_name), NULL, class_init }; \ CRuntimeClass* class_name::GetRuntimeClass() const \ { return RUNTIME_CLASS(class_name); } #endif
首先来看“AFX_COMDAT const CRuntimeClass class_name::class##class_name = {#class_name, sizeof(class class_name), wSchema, pfnNew, &class_name::_GetBaseClass, NULL, class_init }; ”语句，给之前在DECLARE_DYNAMIC里定义的CRuntimeClass类型的静态成员变量赋。

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