時(shí)間的痕跡

一.概述

CArchive使用了緩沖區(qū)，即一段內(nèi)存空間作為臨時(shí)數(shù)據(jù)存儲(chǔ)地，對(duì)CArchive的讀寫都先依次排列到此緩沖區(qū)，當(dāng)緩沖區(qū)滿或用戶要求時(shí)，將此段整理后的數(shù)據(jù)讀寫到指定的存儲(chǔ)煤質(zhì)。
當(dāng)建立CArchive對(duì)象時(shí)，應(yīng)指定其模式是用于緩沖區(qū)讀，還是用于緩沖區(qū)寫。
可以這樣理解，CArchive對(duì)象相當(dāng)于鐵路的貨運(yùn)練調(diào)度站，零散的貨物被收集，當(dāng)總量到達(dá)火車運(yùn)量的時(shí)候，由火車裝運(yùn)走。
當(dāng)接到火車的貨物時(shí)，則貨物由被分散到各自的貨主。與貨運(yùn)不同的是，交貨、取貨是按時(shí)間循序執(zhí)行的，而不是憑票據(jù)。因此必須保證送貨的和取貨的貨主按同樣的循序去存或取。
對(duì)于大型的貨物，則是拆散成火車單位，運(yùn)走，取貨時(shí)，依次取各部分，組裝成原物。

二.內(nèi)部數(shù)據(jù)
緩沖區(qū)指針 BYTE* m_lpBufStart,指向緩沖區(qū)，這個(gè)緩沖區(qū)有可能是底層CFile(如派生類CMemFile)對(duì)象提供的，但一般是CArchive自己建立的。
緩沖區(qū)尾部指針 BYTE* m_lpBufMax;
緩沖區(qū)當(dāng)前位置指針 BYTE* m_lpBufCur;
初始化時(shí)，如果是讀模式,當(dāng)前位置在尾部，如果是寫模式，當(dāng)前位置在頭部:

m_lpBufCur = (IsLoading()) ? m_lpBufMax : m_lpBufStart;

三.基本數(shù)據(jù)讀寫

對(duì)于基本的數(shù)據(jù)類型，例如字節(jié)、雙字等，可以直接使用">>"、"<<"符號(hào)進(jìn)行讀出、寫入。

//操作符定義捕:
	
//插入操作
CArchive& operator<<(BYTE by);
CArchive& operator<<(WORD w);
CArchive& operator<<(LONG l);
CArchive& operator<<(DWORD dw);
CArchive& operator<<(float f);
CArchive& operator<<(double d);
CArchive& operator<<(int i);
CArchive& operator<<(short w);
CArchive& operator<<(char ch);
CArchive& operator<<(unsigned u);

//提取操作
CArchive& operator>>(BYTE& by);
CArchive& operator>>(WORD& w);
CArchive& operator>>(DWORD& dw);
CArchive& operator>>(LONG& l);
CArchive& operator>>(float& f);
CArchive& operator>>(double& d);

CArchive& operator>>(int& i);
CArchive& operator>>(short& w);
CArchive& operator>>(char& ch);
CArchive& operator>>(unsigned& u);

下面以雙字為例，分析原碼

雙字的插入(寫)

CArchive& CArchive::operator<<(DWORD dw)
{
	if (m_lpBufCur + sizeof(DWORD) > m_lpBufMax) //緩沖區(qū)空間不夠
		Flush();  //緩沖區(qū)內(nèi)容提交到實(shí)際存儲(chǔ)煤質(zhì)。

	if (!(m_nMode & bNoByteSwap))
		_AfxByteSwap(dw, m_lpBufCur);  //處理字節(jié)順序
	else
		*(DWORD*)m_lpBufCur = dw;      //添入緩沖區(qū)

	m_lpBufCur += sizeof(DWORD); 	   //移動(dòng)當(dāng)前指針
	return *this;
}

雙字的提取(讀)

CArchive& CArchive::operator>>(DWORD& dw)
{
	if (m_lpBufCur + sizeof(DWORD) > m_lpBufMax) //緩沖區(qū)要讀完了
		FillBuffer(sizeof(DWORD) - (UINT)(m_lpBufMax - m_lpBufCur));  //重新讀入內(nèi)容到緩沖區(qū)

	dw = *(DWORD*)m_lpBufCur;		//讀取雙字
	m_lpBufCur += sizeof(DWORD);	//移動(dòng)當(dāng)前位置指針

	if (!(m_nMode & bNoByteSwap))
		_AfxByteSwap(dw, (BYTE*)&dw);  //處理字節(jié)順序
	return *this;
}

四.緩沖區(qū)的更新

以上操作中，當(dāng)緩沖區(qū)將插入滿或緩沖區(qū)將提取空時(shí)，都將對(duì)緩沖區(qū)進(jìn)行更新處理。

緩沖區(qū)將插入滿時(shí)調(diào)用Flush();

void CArchive::Flush()
{
	ASSERT_VALID(m_pFile);
	ASSERT(m_bDirectBuffer || m_lpBufStart != NULL);
	ASSERT(m_bDirectBuffer || m_lpBufCur != NULL);
	ASSERT(m_lpBufStart == NULL ||
		AfxIsValidAddress(m_lpBufStart, m_lpBufMax - m_lpBufStart, IsStoring()));
	ASSERT(m_lpBufCur == NULL ||
		AfxIsValidAddress(m_lpBufCur, m_lpBufMax - m_lpBufCur, IsStoring()));

	if (IsLoading())
	{
		// unget the characters in the buffer, seek back unused amount
		if (m_lpBufMax != m_lpBufCur)
			m_pFile-> Seek(-(m_lpBufMax - m_lpBufCur), CFile::current);
		m_lpBufCur = m_lpBufMax;    // 指向尾
	}
	else   //寫模式
	{
		if (!m_bDirectBuffer)
		{
			// 內(nèi)容寫入到文件
			if (m_lpBufCur != m_lpBufStart)
				m_pFile-> Write(m_lpBufStart, m_lpBufCur - m_lpBufStart);
		}
		else
		{
			//如果是直接針對(duì)內(nèi)存區(qū)域的的(例如CMemFile中) (只需移動(dòng)相關(guān)指針，指向新的一塊內(nèi)存)
			if (m_lpBufCur != m_lpBufStart)
				m_pFile-> GetBufferPtr(CFile::bufferCommit, m_lpBufCur - m_lpBufStart);
			// get next buffer
			VERIFY(m_pFile-> GetBufferPtr(CFile::bufferWrite, m_nBufSize,
				(void**)&m_lpBufStart, (void**)&m_lpBufMax) == (UINT)m_nBufSize);
			ASSERT((UINT)m_nBufSize == (UINT)(m_lpBufMax - m_lpBufStart));
		}
		m_lpBufCur = m_lpBufStart; //指向緩沖區(qū)首
	}
}

緩沖區(qū)將提取空,會(huì)調(diào)用FillBuffer。 nBytesNeeded為當(dāng)前剩余部分上尚有用的字節(jié)

void CArchive::FillBuffer(UINT nBytesNeeded)
{
	ASSERT_VALID(m_pFile);
	ASSERT(IsLoading());
	ASSERT(m_bDirectBuffer || m_lpBufStart != NULL);
	ASSERT(m_bDirectBuffer || m_lpBufCur != NULL);
	ASSERT(nBytesNeeded > 0);
	ASSERT(nBytesNeeded <= (UINT)m_nBufSize);
	ASSERT(m_lpBufStart == NULL ||
		AfxIsValidAddress(m_lpBufStart, m_lpBufMax - m_lpBufStart, FALSE));
	ASSERT(m_lpBufCur == NULL ||
		AfxIsValidAddress(m_lpBufCur, m_lpBufMax - m_lpBufCur, FALSE));

	UINT nUnused = m_lpBufMax - m_lpBufCur;
	ULONG nTotalNeeded = ((ULONG)nBytesNeeded) + nUnused;

	// 從文件中讀取
	if (!m_bDirectBuffer)
	{
		ASSERT(m_lpBufCur != NULL);
		ASSERT(m_lpBufStart != NULL);
		ASSERT(m_lpBufMax != NULL);

		if (m_lpBufCur > m_lpBufStart)
		{
			//保留剩余的尚未處理的部分，將它們移動(dòng)到頭
			if ((int)nUnused > 0)
			{
				memmove(m_lpBufStart, m_lpBufCur, nUnused);
				m_lpBufCur = m_lpBufStart;
				m_lpBufMax = m_lpBufStart + nUnused;
			}

			// read to satisfy nBytesNeeded or nLeft if possible
			UINT nRead = nUnused;
			UINT nLeft = m_nBufSize-nUnused;
			UINT nBytes;
			BYTE* lpTemp = m_lpBufStart + nUnused;
			do
			{
				nBytes = m_pFile-> Read(lpTemp, nLeft);
				lpTemp = lpTemp + nBytes;
				nRead += nBytes;
				nLeft -= nBytes;
			}
			while (nBytes > 0 && nLeft > 0 && nRead < nBytesNeeded);

			m_lpBufCur = m_lpBufStart;
			m_lpBufMax = m_lpBufStart + nRead;
		}
	}
	else
	{
		// 如果是針對(duì)內(nèi)存區(qū)域(CMemFile),移動(dòng)相關(guān)指針，指向新的一塊內(nèi)存
		if (nUnused != 0)
			m_pFile-> Seek(-(LONG)nUnused, CFile::current);
		UINT nActual = m_pFile-> GetBufferPtr(CFile::bufferRead, m_nBufSize,
			(void**)&m_lpBufStart, (void**)&m_lpBufMax);
		ASSERT(nActual == (UINT)(m_lpBufMax - m_lpBufStart));
		m_lpBufCur = m_lpBufStart;
	}

	// not enough data to fill request?
	if ((ULONG)(m_lpBufMax - m_lpBufCur) < nTotalNeeded)
		AfxThrowArchiveException(CArchiveException::endOfFile);
}

五.指定長度數(shù)據(jù)段落的讀寫

以下分析
UINT Read(void* lpBuf, UINT nMax); 讀取長度為nMax的數(shù)據(jù)
void Write(const void* lpBuf, UINT nMax); 寫入指定長度nMax的數(shù)據(jù)
對(duì)于大段數(shù)據(jù)的讀寫，先使用當(dāng)前緩沖區(qū)中的內(nèi)容或空間讀取或?qū)懭耄暨@些空間夠用了，則結(jié)束。
否則，從剩余的數(shù)據(jù)中找出最大的緩沖區(qū)整數(shù)倍大小的一塊數(shù)據(jù)，直接讀寫到存儲(chǔ)煤質(zhì)(不反復(fù)使用緩沖區(qū))。
剩余的余數(shù)部分，再使用緩沖區(qū)讀寫。
(說明:緩沖區(qū)讀寫的主要目的是將零散的數(shù)據(jù)以緩沖區(qū)大小為尺度來處理。對(duì)于大型數(shù)據(jù)，其中間的部分，不是零散的數(shù)據(jù)，使用緩沖區(qū)已經(jīng)沒有意思，故直接讀寫)

①讀取

UINT CArchive::Read(void* lpBuf, UINT nMax)
{
	ASSERT_VALID(m_pFile);
	if (nMax == 0)
		return 0;

	UINT nMaxTemp = nMax;  //還需要讀入的長度，讀入一部分，就減相應(yīng)數(shù)值，直到此數(shù)值變?yōu)榱?
	
	//處理當(dāng)前緩沖區(qū)中剩余部分。
	//如果要求讀入字節(jié)小于緩沖區(qū)中剩余部分,則第一部分為要求讀入的字節(jié)數(shù)，
	//否則讀入全部剩余部分	
	UINT nTemp = min(nMaxTemp, (UINT)(m_lpBufMax - m_lpBufCur));   
	memcpy(lpBuf, m_lpBufCur, nTemp);
	m_lpBufCur += nTemp;
	lpBuf = (BYTE*)lpBuf + nTemp; //移動(dòng)讀出內(nèi)容所在區(qū)域的指針
	nMaxTemp -= nTemp;

	//當(dāng)前緩沖區(qū)中剩余部分不夠要求讀入的長度。
	//還有字節(jié)需要讀，則需要根據(jù)需要執(zhí)行若干次填充緩沖區(qū)，讀出，直到讀出指定字節(jié)。
	if (nMaxTemp != 0)  
	{
		//計(jì)算出去除尾數(shù)部分的字節(jié)大小(整數(shù)個(gè)緩沖區(qū)大小) 
		//對(duì)于這些部分，字節(jié)從文件對(duì)象中讀出，放到輸出緩沖區(qū)
		nTemp = nMaxTemp - (nMaxTemp % m_nBufSize);  
		UINT nRead = 0;

		UINT nLeft = nTemp;
		UINT nBytes;
		do
		{
			nBytes = m_pFile-> Read(lpBuf, nLeft); //要求讀入此整數(shù)緩沖區(qū)部分大小
			lpBuf = (BYTE*)lpBuf + nBytes;
			nRead += nBytes;
			nLeft -= nBytes;
		}
		while ((nBytes > 0) && (nLeft > 0)); 知道讀入了預(yù)定大小，或到達(dá)文件尾

		nMaxTemp -= nRead;

		if (nRead == nTemp) //讀入的字節(jié)等于讀入的整數(shù)倍部分  該讀最后的余數(shù)部分了
		{
			// 建立裝有此最后余數(shù)部分的內(nèi)容的CArchive的工作緩沖區(qū)。
			if (!m_bDirectBuffer)
			{
				UINT nLeft = max(nMaxTemp, (UINT)m_nBufSize);
				UINT nBytes;
				BYTE* lpTemp = m_lpBufStart;
				nRead = 0;
				do
				{
					nBytes = m_pFile-> Read(lpTemp, nLeft);  //從文件中讀入到CArchive緩沖區(qū)
					lpTemp = lpTemp + nBytes;
					nRead += nBytes;
					nLeft -= nBytes;
				}
				while ((nBytes > 0) && (nLeft > 0) && nRead < nMaxTemp);

				m_lpBufCur = m_lpBufStart;
				m_lpBufMax = m_lpBufStart + nRead;
			}
			else
			{
				nRead = m_pFile-> GetBufferPtr(CFile::bufferRead, m_nBufSize,
					(void**)&m_lpBufStart, (void**)&m_lpBufMax);
				ASSERT(nRead == (UINT)(m_lpBufMax - m_lpBufStart));
				m_lpBufCur = m_lpBufStart;
			}

			//讀出此剩余部分到輸出
			nTemp = min(nMaxTemp, (UINT)(m_lpBufMax - m_lpBufCur));
			memcpy(lpBuf, m_lpBufCur, nTemp);
			m_lpBufCur += nTemp;
			nMaxTemp -= nTemp;
		}
		
	}
	return nMax - nMaxTemp;
}

②保存,寫入

void CArchive::Write(const void* lpBuf, UINT nMax)
{
	if (nMax == 0)
		return;
	
	//讀入可能的部分到緩沖區(qū)當(dāng)前的剩余部分	
	UINT nTemp = min(nMax, (UINT)(m_lpBufMax - m_lpBufCur));
	memcpy(m_lpBufCur, lpBuf, nTemp);
	m_lpBufCur += nTemp;
	lpBuf = (BYTE*)lpBuf + nTemp;
	nMax -= nTemp;

	if (nMax > 0)  //還有未寫入的部分
	{
		Flush();    //將當(dāng)前緩沖區(qū)寫入到存儲(chǔ)煤質(zhì)

		//計(jì)算出整數(shù)倍緩沖區(qū)大小的字節(jié)數(shù)
		nTemp = nMax - (nMax % m_nBufSize);
		m_pFile-> Write(lpBuf, nTemp);  //直接寫到文件
		lpBuf = (BYTE*)lpBuf + nTemp;
		nMax -= nTemp;


		//剩余部分添加到緩沖區(qū)
		if (m_bDirectBuffer)
		{
			// sync up direct mode buffer to new file position
			VERIFY(m_pFile-> GetBufferPtr(CFile::bufferWrite, m_nBufSize,
				(void**)&m_lpBufStart, (void**)&m_lpBufMax) == (UINT)m_nBufSize);
			ASSERT((UINT)m_nBufSize == (UINT)(m_lpBufMax - m_lpBufStart));
			m_lpBufCur = m_lpBufStart;
		}

		// copy remaining to active buffer
		ASSERT(nMax < (UINT)m_nBufSize);
		ASSERT(m_lpBufCur == m_lpBufStart);
		memcpy(m_lpBufCur, lpBuf, nMax);
		m_lpBufCur += nMax;
	}
}

六.字符串的讀寫

①CArchive提供的WriteString和ReadString

字符串寫

void CArchive::WriteString(LPCTSTR lpsz)
{
	ASSERT(AfxIsValidString(lpsz));
	Write(lpsz, lstrlen(lpsz) * sizeof(TCHAR));  //調(diào)用Write，將字符串對(duì)應(yīng)的一段數(shù)據(jù)寫入
}

字符串讀(讀取一行字符串)

LPTSTR CArchive::ReadString(LPTSTR lpsz, UINT nMax)
{
	// if nMax is negative (such a large number doesn''t make sense given today''s
	// 2gb address space), then assume it to mean "keep the newline".
	int nStop = (int)nMax < 0 ? -(int)nMax : (int)nMax;
	ASSERT(AfxIsValidAddress(lpsz, (nStop+1) * sizeof(TCHAR)));

	_TUCHAR ch;
	int nRead = 0;

	TRY
	{
		while (nRead < nStop)
		{
			*this >> ch;  //讀出一個(gè)字節(jié)

			// stop and end-of-line (trailing ''\n'' is ignored)  遇換行—回車
			if (ch == ''\n'' || ch == ''\r'')
			{
				if (ch == ''\r'')
					*this >> ch;
				// store the newline when called with negative nMax
				if ((int)nMax != nStop)
					lpsz[nRead++] = ch;
				break;
			}
			lpsz[nRead++] = ch;
		}
	}
	CATCH(CArchiveException, e)
	{
		if (e-> m_cause == CArchiveException::endOfFile)
		{
			DELETE_EXCEPTION(e);
			if (nRead == 0)
				return NULL;
		}
		else
		{
			THROW_LAST();
		}
	}
	END_CATCH

	lpsz[nRead] = ''\0'';
	return lpsz;
}

ReadString到CString對(duì)象,可以多行字符

BOOL CArchive::ReadString(CString& rString)
{
	rString = &afxChNil;    // empty string without deallocating
	const int nMaxSize = 128;
	LPTSTR lpsz = rString.GetBuffer(nMaxSize);
	LPTSTR lpszResult;
	int nLen;
	for (;;)
	{
		lpszResult = ReadString(lpsz, (UINT)-nMaxSize); // store the newline
		rString.ReleaseBuffer();

		// if string is read completely or EOF
		if (lpszResult == NULL ||
			(nLen = lstrlen(lpsz)) < nMaxSize ||
			lpsz[nLen-1] == ''\n'')
		{
			break;
		}

		nLen = rString.GetLength();
		lpsz = rString.GetBuffer(nMaxSize + nLen) + nLen;
	}

	// remove ''\n'' from end of string if present
	lpsz = rString.GetBuffer(0);
	nLen = rString.GetLength();
	if (nLen != 0 && lpsz[nLen-1] == ''\n'')
		rString.GetBufferSetLength(nLen-1);

	return lpszResult != NULL;
}

②使用CString對(duì)象的"<<"與">>"符讀寫字符串

CString定義了輸入輸出符,可以象基本類型的數(shù)據(jù)一樣使用CArchive 的操作符定義

friend CArchive& AFXAPI operator<<(CArchive& ar, const CString& string);
friend CArchive& AFXAPI operator>>(CArchive& ar, CString& string);

// CString serialization code
// String format:
//      UNICODE strings are always prefixed by 0xff, 0xfffe
//      if < 0xff chars: len:BYTE, TCHAR chars
//      if >= 0xff characters: 0xff, len:WORD, TCHAR chars
//      if >= 0xfffe characters: 0xff, 0xffff, len:DWORD, TCHARs

CArchive& AFXAPI operator<<(CArchive& ar, const CString& string)
{
	// special signature to recognize unicode strings
#ifdef _UNICODE
	ar << (BYTE)0xff;
	ar << (WORD)0xfffe;
#endif

	if (string.GetData()-> nDataLength < 255)
	{
		ar << (BYTE)string.GetData()-> nDataLength;
	}
	else if (string.GetData()-> nDataLength < 0xfffe)
	{
		ar << (BYTE)0xff;
		ar << (WORD)string.GetData()-> nDataLength;
	}
	else
	{
		ar << (BYTE)0xff;
		ar << (WORD)0xffff;
		ar << (DWORD)string.GetData()-> nDataLength;
	}
	ar.Write(string.m_pchData, string.GetData()-> nDataLength*sizeof(TCHAR));
	return ar;
}

// return string length or -1 if UNICODE string is found in the archive
AFX_STATIC UINT AFXAPI _AfxReadStringLength(CArchive& ar)
{
	DWORD nNewLen;

	// attempt BYTE length first
	BYTE bLen;
	ar >> bLen;

	if (bLen < 0xff)
		return bLen;

	// attempt WORD length
	WORD wLen;
	ar >> wLen;
	if (wLen == 0xfffe)
	{
		// UNICODE string prefix (length will follow)
		return (UINT)-1;
	}
	else if (wLen == 0xffff)
	{
		// read DWORD of length
		ar >> nNewLen;
		return (UINT)nNewLen;
	}
	else
		return wLen;
}

CArchive& AFXAPI operator>>(CArchive& ar, CString& string)
{
#ifdef _UNICODE
	int nConvert = 1;   // if we get ANSI, convert
#else
	int nConvert = 0;   // if we get UNICODE, convert
#endif

	UINT nNewLen = _AfxReadStringLength(ar);
	if (nNewLen == (UINT)-1)
	{
		nConvert = 1 - nConvert;
		nNewLen = _AfxReadStringLength(ar);
		ASSERT(nNewLen != -1);
	}

	// set length of string to new length
	UINT nByteLen = nNewLen;
#ifdef _UNICODE
	string.GetBufferSetLength((int)nNewLen);
	nByteLen += nByteLen * (1 - nConvert);  // bytes to read
#else
	nByteLen += nByteLen * nConvert;    // bytes to read
	if (nNewLen == 0)
		string.GetBufferSetLength(0);
	else
		string.GetBufferSetLength((int)nByteLen+nConvert);
#endif

	// read in the characters
	if (nNewLen != 0)
	{
		ASSERT(nByteLen != 0);

		// read new data
		if (ar.Read(string.m_pchData, nByteLen) != nByteLen)
			AfxThrowArchiveException(CArchiveException::endOfFile);

		// convert the data if as necessary
		if (nConvert != 0)
		{
#ifdef _UNICODE
			CStringData* pOldData = string.GetData();
			LPSTR lpsz = (LPSTR)string.m_pchData;
#else
			CStringData* pOldData = string.GetData();
			LPWSTR lpsz = (LPWSTR)string.m_pchData;
#endif
			lpsz[nNewLen] = ''\0'';    // must be NUL terminated
			string.Init();   // don''t delete the old data
			string = lpsz;   // convert with operator=(LPWCSTR)
			CString::FreeData(pOldData);
		}
	}
	return ar;
}

七.CObject派生對(duì)象的讀寫

MFC中多數(shù)類都從CObject類派生，CObject類與CArchive類有著良好的合作關(guān)系，能實(shí)現(xiàn)將對(duì)象序列化儲(chǔ)存到文件或其他媒介中去，或者讀取預(yù)先儲(chǔ)存的對(duì)象，動(dòng)態(tài)建立對(duì)象等功能。

①CObject定義了針對(duì)CArvhive的輸入輸出操作符,可以向其他基本數(shù)據(jù)類型一樣使用"<<"、"<<"符號(hào)

CArchive& AFXAPI operator<<(CArchive& ar, const CObject* pOb)
	{ ar.WriteObject(pOb); return ar; }
CArchive& AFXAPI operator>>(CArchive& ar, CObject*& pOb)
	{ pOb = ar.ReadObject(NULL); return ar; }

當(dāng)使用這些符號(hào)時(shí)，實(shí)際上執(zhí)行的是CArchive的WriteObject和ReadObject成員

②WriteObject與ReadObject

在WriteObject與ReadObject中先寫入或讀取運(yùn)行時(shí)類信息(CRuntimeClas)，再調(diào)用Serialze(..),按其中的代碼讀寫具體的對(duì)象數(shù)據(jù)。

因此，只要在CObject派生類中重載Serilize()函數(shù)，寫入具體的讀寫過程，就可以使對(duì)象具有存儲(chǔ)與創(chuàng)建能力。

//將對(duì)象寫入到緩沖區(qū)
void CArchive::WriteObject(const CObject* pOb)
{
	DWORD nObIndex;
	// make sure m_pStoreMap is initialized
	MapObject(NULL);

	if (pOb == NULL)
	{
		// save out null tag to represent NULL pointer
		*this << wNullTag;
	}
	else if ((nObIndex = (DWORD)(*m_pStoreMap)[(void*)pOb]) != 0)
		// assumes initialized to 0 map
	{
		// save out index of already stored object
		if (nObIndex < wBigObjectTag)
			*this << (WORD)nObIndex;
		else
		{
			*this << wBigObjectTag;
			*this << nObIndex;
		}
	}
	else
	{
		// write class of object first
		CRuntimeClass* pClassRef = pOb-> GetRuntimeClass();
		WriteClass(pClassRef);  //寫入運(yùn)行類信息

		// enter in stored object table, checking for overflow
		CheckCount();
		(*m_pStoreMap)[(void*)pOb] = (void*)m_nMapCount++;

		// 調(diào)用CObject的Serialize成員，按其中的代碼寫入類中數(shù)據(jù)。
		((CObject*)pOb)-> Serialize(*this);
	}
}

CObject* CArchive::ReadObject(const CRuntimeClass* pClassRefRequested)
{

	// attempt to load next stream as CRuntimeClass
	UINT nSchema;
	DWORD obTag;
	//先讀入運(yùn)行時(shí)類信息
	CRuntimeClass* pClassRef = ReadClass(pClassRefRequested, &nSchema, &obTag);

	// check to see if tag to already loaded object
	CObject* pOb;
	if (pClassRef == NULL)
	{
		if (obTag > (DWORD)m_pLoadArray-> GetUpperBound())
		{
			// tag is too large for the number of objects read so far
			AfxThrowArchiveException(CArchiveException::badIndex,
				m_strFileName);
		}

		pOb = (CObject*)m_pLoadArray-> GetAt(obTag);
		if (pOb != NULL && pClassRefRequested != NULL &&
			 !pOb-> IsKindOf(pClassRefRequested))
		{
			// loaded an object but of the wrong class
			AfxThrowArchiveException(CArchiveException::badClass,
				m_strFileName);
		}
	}
	else
	{
		// 建立對(duì)象
		pOb = pClassRef-> CreateObject();
		if (pOb == NULL)
			AfxThrowMemoryException();

		// Add to mapping array BEFORE de-serializing
		CheckCount();
		m_pLoadArray-> InsertAt(m_nMapCount++, pOb);

		// Serialize the object with the schema number set in the archive
		UINT nSchemaSave = m_nObjectSchema;
		m_nObjectSchema = nSchema;
		pOb-> Serialize(*this); //調(diào)用CObject的Serialize,按其中代碼讀入對(duì)象數(shù)據(jù)。
		m_nObjectSchema = nSchemaSave;
		ASSERT_VALID(pOb);
	}

	return pOb;
}

③運(yùn)行時(shí)類信息的讀寫

為了避免眾多重復(fù)的同類對(duì)象寫入重復(fù)的類信息，CArchive中使用CMap對(duì)象儲(chǔ)存和檢索類信息。

void CArchive::WriteClass(const CRuntimeClass* pClassRef)
{
	ASSERT(pClassRef != NULL);
	ASSERT(IsStoring());    // proper direction

	if (pClassRef-> m_wSchema == 0xFFFF)
	{
		TRACE1("Warning: Cannot call WriteClass/WriteObject for %hs.\n",
			pClassRef-> m_lpszClassName);
		AfxThrowNotSupportedException();
	}

	// make sure m_pStoreMap is initialized
	MapObject(NULL);

	// write out class id of pOb, with high bit set to indicate
	// new object follows

	// ASSUME: initialized to 0 map
	DWORD nClassIndex;
	if ((nClassIndex = (DWORD)(*m_pStoreMap)[(void*)pClassRef]) != 0)
	{
		// previously seen class, write out the index tagged by high bit
		if (nClassIndex < wBigObjectTag)
			*this << (WORD)(wClassTag | nClassIndex);
		else
		{
			*this << wBigObjectTag;
			*this << (dwBigClassTag | nClassIndex);
		}
	}
	else
	{
		// store new class
		*this << wNewClassTag;
		pClassRef-> Store(*this);

		// store new class reference in map, checking for overflow
		CheckCount();
		(*m_pStoreMap)[(void*)pClassRef] = (void*)m_nMapCount++;
	}
}

CRuntimeClass* CArchive::ReadClass(const CRuntimeClass* pClassRefRequested,
	UINT* pSchema, DWORD* pObTag)
{
	ASSERT(pClassRefRequested == NULL ||
		AfxIsValidAddress(pClassRefRequested, sizeof(CRuntimeClass), FALSE));
	ASSERT(IsLoading());    // proper direction

	if (pClassRefRequested != NULL && pClassRefRequested-> m_wSchema == 0xFFFF)
	{
		TRACE1("Warning: Cannot call ReadClass/ReadObject for %hs.\n",
			pClassRefRequested-> m_lpszClassName);
		AfxThrowNotSupportedException();
	}

	// make sure m_pLoadArray is initialized
	MapObject(NULL);

	// read object tag - if prefixed by wBigObjectTag then DWORD tag follows
	DWORD obTag;
	WORD wTag;
	*this >> wTag;
	if (wTag == wBigObjectTag)
		*this >> obTag;
	else
		obTag = ((wTag & wClassTag) << 16) | (wTag & ~wClassTag);

	// check for object tag (throw exception if expecting class tag)
	if (!(obTag & dwBigClassTag))
	{
		if (pObTag == NULL)
			AfxThrowArchiveException(CArchiveException::badIndex, m_strFileName);

		*pObTag = obTag;
		return NULL;
	}

	CRuntimeClass* pClassRef;
	UINT nSchema;
	if (wTag == wNewClassTag)
	{
		// new object follows a new class id
		if ((pClassRef = CRuntimeClass::Load(*this, &nSchema)) == NULL)
			AfxThrowArchiveException(CArchiveException::badClass, m_strFileName);

		// check nSchema against the expected schema
		if ((pClassRef-> m_wSchema & ~VERSIONABLE_SCHEMA) != nSchema)
		{
			if (!(pClassRef-> m_wSchema & VERSIONABLE_SCHEMA))
			{
				// schema doesn''t match and not marked as VERSIONABLE_SCHEMA
				AfxThrowArchiveException(CArchiveException::badSchema,
					m_strFileName);
			}
			else
			{
				// they differ -- store the schema for later retrieval
				if (m_pSchemaMap == NULL)
					m_pSchemaMap = new CMapPtrToPtr;
				ASSERT_VALID(m_pSchemaMap);
				m_pSchemaMap-> SetAt(pClassRef, (void*)nSchema);
			}
		}
		CheckCount();
		m_pLoadArray-> InsertAt(m_nMapCount++, pClassRef);
	}
	else
	{
		// existing class index in obTag followed by new object
		DWORD nClassIndex = (obTag & ~dwBigClassTag);
		if (nClassIndex == 0 || nClassIndex > (DWORD)m_pLoadArray-> GetUpperBound())
			AfxThrowArchiveException(CArchiveException::badIndex,
				m_strFileName);

		pClassRef = (CRuntimeClass*)m_pLoadArray-> GetAt(nClassIndex);
		ASSERT(pClassRef != NULL);

		// determine schema stored against objects of this type
		void* pTemp;
		BOOL bFound = FALSE;
		nSchema = 0;
		if (m_pSchemaMap != NULL)
		{
			bFound = m_pSchemaMap-> Lookup( pClassRef, pTemp );
			if (bFound)
				nSchema = (UINT)pTemp;
		}
		if (!bFound)
			nSchema = pClassRef-> m_wSchema & ~VERSIONABLE_SCHEMA;
   }

	// check for correct derivation
	if (pClassRefRequested != NULL &&
		!pClassRef-> IsDerivedFrom(pClassRefRequested))
	{
		AfxThrowArchiveException(CArchiveException::badClass, m_strFileName);
	}

	// store nSchema for later examination
	if (pSchema != NULL)
		*pSchema = nSchema;
	else
		m_nObjectSchema = nSchema;

	// store obTag for later examination
	if (pObTag != NULL)
		*pObTag = obTag;

	// return the resulting CRuntimeClass*
	return pClassRef;
}