一.概述
CArchive使用了緩沖區，即一段內存空間作為臨時數據存儲地，對CArchive的讀寫都先依次排列到此緩沖區，當緩沖區滿或用戶要求時，將此段整理后的數據讀寫到指定的存儲煤質。
當建立CArchive對象時，應指定其模式是用于緩沖區讀，還是用于緩沖區寫。
可以這樣理解，CArchive對象相當于鐵路的貨運練調度站，零散的貨物被收集，當總量到達火車運量的時候，由火車裝運走。
當接到火車的貨物時，則貨物由被分散到各自的貨主。與貨運不同的是，交貨、取貨是按時間循序執行的，而不是憑票據。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。
對于大型的貨物，則是拆散成火車單位，運走，取貨時，依次取各部分，組裝成原物。
二.內部數據
緩沖區指針 BYTE* m_lpBufStart,指向緩沖區，這個緩沖區有可能是底層CFile(如派生類CMemFile)對象提供的，但一般是CArchive自己建立的。
緩沖區尾部指針 BYTE* m_lpBufMax;
緩沖區當前位置指針 BYTE* m_lpBufCur;
初始化時，如果是讀模式,當前位置在尾部，如果是寫模式，當前位置在頭部:
m_lpBufCur = (IsLoading()) ? m_lpBufMax : m_lpBufStart;
三.基本數據讀寫 對于基本的數據類型，例如字節、雙字等，可以直接使用">>"、"<<"符號進行讀出、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) //緩沖區空間不夠
Flush(); //緩沖區內容提交到實際存儲煤質。
if (!(m_nMode & bNoByteSwap))
_AfxByteSwap(dw, m_lpBufCur); //處理字節順序
else
*(DWORD*)m_lpBufCur = dw; //添入緩沖區
m_lpBufCur += sizeof(DWORD); //移動當前指針
return *this;
}
雙字的提取(讀)CArchive& CArchive::operator>>(DWORD& dw)
{
if (m_lpBufCur + sizeof(DWORD) > m_lpBufMax) //緩沖區要讀完了
FillBuffer(sizeof(DWORD) - (UINT)(m_lpBufMax - m_lpBufCur)); //重新讀入內容到緩沖區
dw = *(DWORD*)m_lpBufCur; //讀取雙字
m_lpBufCur += sizeof(DWORD); //移動當前位置指針
if (!(m_nMode & bNoByteSwap))
_AfxByteSwap(dw, (BYTE*)&dw); //處理字節順序
return *this;
}
四.緩沖區的更新以上操作中，當緩沖區將插入滿或緩沖區將提取空時，都將對緩沖區進行更新處理。
緩沖區將插入滿時調用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
{
//如果是直接針對內存區域的的(例如CMemFile中) (只需移動相關指針，指向新的一塊內存)
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; //指向緩沖區首
}
}緩沖區將提取空,會調用FillBuffer。 nBytesNeeded為當前剩余部分上尚有用的字節
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
{
// 如果是針對內存區域(CMemFile),移動相關指針，指向新的一塊內存
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.指定長度數據段落的讀寫以下分析
UINT Read(void* lpBuf, UINT nMax); 讀取長度為nMax的數據
void Write(const void* lpBuf, UINT nMax); 寫入指定長度nMax的數據
對于大段數據的讀寫，先使用當前緩沖區中的內容或空間讀取或寫入，若這些空間夠用了，則結束。
否則，從剩余的數據中找出最大的緩沖區整數倍大小的一塊數據，直接讀寫到存儲煤質(不反復使用緩沖區)。
剩余的余數部分，再使用緩沖區讀寫。
(說明:緩沖區讀寫的主要目的是將零散的數據以緩沖區大小為尺度來處理。對于大型數據，其中間的部分，不是零散的數據，使用緩沖區已經沒有意思，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，就減相應數值，直到此數值變為零
//處理當前緩沖區中剩余部分。
//如果要求讀入字節小于緩沖區中剩余部分,則第一部分為要求讀入的字節數，
//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; //移動讀出內容所在區域的指針
nMaxTemp -= nTemp;
//當前緩沖區中剩余部分不夠要求讀入的長度。
//還有字節需要讀，則需要根據需要執行若干次填充緩沖區，讀出，直到讀出指定字節。
if (nMaxTemp != 0)
{
//計算出去除尾數部分的字節大小(整數個緩沖區大小)
//對于這些部分，字節從文件對象中讀出，放到輸出緩沖區
nTemp = nMaxTemp - (nMaxTemp % m_nBufSize);
UINT nRead = 0;
UINT nLeft = nTemp;
UINT nBytes;
do
{
nBytes = m_pFile-> Read(lpBuf, nLeft); //要求讀入此整數緩沖區部分大小
lpBuf = (BYTE*)lpBuf + nBytes;
nRead += nBytes;
nLeft -= nBytes;
}
while ((nBytes > 0) && (nLeft > 0)); 知道讀入了預定大小，或到達文件尾
nMaxTemp -= nRead;
if (nRead == nTemp) //讀入的字節等于讀入的整數倍部分 該讀最后的余數部分了
{
// 建立裝有此最后余數部分的內容的CArchive的工作緩沖區。
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
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當前的剩余部分
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(); //將當前緩沖區寫入到存儲煤質
//計算出整數倍緩沖區大小的字節數
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
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)); //調用Write，將字符串對應的一段數據寫入
}
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; //讀出一個字節
// 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據一樣使用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派生對象的讀寫 MFC中多數類都從CObject類派生，CObject類與CArchive類有著良好的合作關系，能實現將對象序列化儲存到文件或其他媒介中去，或者讀取預先儲存的對象，動態建立對象等功能。
①CObject定義了針對CArvhive的輸入輸出操作符,可以向其他基本數據類型一樣使用"<<"、"<<"符號
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; }
當使用這些符號時，實際上執行的是CArchive的WriteObject和ReadObject成員
②WriteObject與ReadObject
在WriteObject與ReadObject中先寫入或讀取運行時類信息(CRuntimeClas)，再調用Serialze(..),按其中的代碼讀寫具體的對象數據。
因此，只要在CObject派生類中重載Serilize()函數，寫入具體的讀寫過程，就可以使對象具有存儲與創建能力。
//將對象寫入到緩沖區
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); //寫入運行類信息
// enter in stored object table, checking for overflow
CheckCount();
(*m_pStoreMap)[(void*)pOb] = (void*)m_nMapCount++;
// 調用CObject的Serialize成員，按其中的代碼寫入類中數據。
((CObject*)pOb)-> Serialize(*this);
}
}
CObject* CArchive::ReadObject(const CRuntimeClass* pClassRefRequested)
{
// attempt to load next stream as CRuntimeClass
UINT nSchema;
DWORD obTag;
//先讀入運行時類信息
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); //調用CObject的Serialize,按其中代碼讀入對象數據。
m_nObjectSchema = nSchemaSave;
ASSERT_VALID(pOb);
}
return pOb;
}
③運行時類信息的讀寫為了避免眾多重復的同類對象寫入重復的類信息，CArchive中使用CMap對象儲存和檢索類信息。
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;
}