首页 > 代码库 > offsetof的意义

offsetof的意义

2024-07-17 14:49:27   225人阅读

offsetof是求类的成员变量的偏移量，如果成员变量是类定义的第一个变量，那他的偏移量应该是0.但是引入继承之后，就要额外考虑了。下面的代码说明了这个问题：

#define AFX_NOVTABLE//#define AFX_NOVTABLE __declspec(novtable)class AFX_NOVTABLE CNoTrackObject{public:    void* PASCAL operator new(size_t nSize);    void PASCAL operator delete(void*);        virtual ~CNoTrackObject() { }};void* PASCAL CNoTrackObject::operator new(size_t nSize){    void* p = ::LocalAlloc(LPTR, nSize);//     if (p == NULL)//         AfxThrowMemoryException();    return p;}void PASCAL CNoTrackObject::operator delete(void* p){    if (p != NULL)        ::LocalFree(p);}struct CThreadData : public CNoTrackObject{    CThreadData* pNext; // required to be member of CSimpleList    int nCount;         // current size of pData    LPVOID* pData;      // actual thread local data (indexed by nSlot)};struct CThreadData2{    CThreadData2* pNext;    int nCount;    LPVOID* pData;};int main(int argc, char* argv[]){    int nOffset = offsetof(CThreadData, pNext);    int nOffset2 = offsetof(CThreadData2, pNext);    return 0;}
View Code

nOffset = 4

nOffset2 = 0


联系
我们