关于CString中辅助结构struct CStringData的疑问

[fredhurui]

struct CStringData
{
long nRefs; // reference count
int nDataLength; // length of data (including terminator)
int nAllocLength; // length of allocation
// TCHAR data[nAllocLength]

TCHAR* data() // TCHAR* to managed data
{ return (TCHAR*)(this+1); }
};
我不太明白
TCHAR* data() // TCHAR* to managed data
{ return (TCHAR*)(this+1); }
中的 return (TCHAR*)(this+1); 这句的意思，望高人指点

[fredhurui]

想了一会儿还是自己写了个测试语句加入了char* data()
char* data() // TCHAR* to managed data
{
cout<<"this ="<<this<<endl;
cout<<"this+1 ="<<this+1<<endl;
return (char*)(this+1);
}

输出this = 0012FF3C
this+1 = 0012FF48
而且siezof(struct CStringData )=12
this+1 - this = 12

[Allen_zhang]

这个你看一下CString的结构就知道了
CString的头就是一个CStringData，接下来就是真正的字符串的值

TCHAR* data()          // TCHAR* to managed data 
{ return (TCHAR*)(this+1); } 

这个就是返回字符串的开始地址。首先是this+1，这样就是往前一个CStringData的长度，
得到这个指针后转换成TCHAR*，这个就是字符串的开始地址。

#define ROUND(x,y) (((x)+(y-1))&~(y-1))
#define ROUND4(x) ROUND(x, 4)
AFX_STATIC CFixedAlloc _afxAlloc64(ROUND4(65*sizeof(TCHAR)+sizeof(CStringData)));
AFX_STATIC CFixedAlloc _afxAlloc128(ROUND4(129*sizeof(TCHAR)+sizeof(CStringData)));
AFX_STATIC CFixedAlloc _afxAlloc256(ROUND4(257*sizeof(TCHAR)+sizeof(CStringData)));
AFX_STATIC CFixedAlloc _afxAlloc512(ROUND4(513*sizeof(TCHAR)+sizeof(CStringData)));

#endif //!_DEBUG

void CString::AllocBuffer(int nLen)
// always allocate one extra character for '\0' termination
// assumes [optimistically] that data length will equal allocation length
{
	ASSERT(nLen >= 0);
	ASSERT(nLen <= INT_MAX-1);    // max size (enough room for 1 extra)

	if (nLen == 0)
		Init();
	else
	{
		CStringData* pData;
#ifndef _DEBUG
		if (nLen <= 64)
		{
			pData = (CStringData*)_afxAlloc64.Alloc();
			pData->nAllocLength = 64;
		}
		else if (nLen <= 128)
		{
			pData = (CStringData*)_afxAlloc128.Alloc();
			pData->nAllocLength = 128;
		}
		else if (nLen <= 256)
		{
			pData = (CStringData*)_afxAlloc256.Alloc();
			pData->nAllocLength = 256;
		}
		else if (nLen <= 512)
		{
			pData = (CStringData*)_afxAlloc512.Alloc();
			pData->nAllocLength = 512;
		}
		else
#endif
		{
			pData = (CStringData*)
				new BYTE[sizeof(CStringData) + (nLen+1)*sizeof(TCHAR)];
			pData->nAllocLength = nLen;
		}
		pData->nRefs = 1;
		pData->data()[nLen] = '\0';
		pData->nDataLength = nLen;
		m_pchData = pData->data();
	}
}

[fredhurui]

这里的高人的确很多