CArchive 原理
MFC 提供CArchive类实现数据的缓冲区读写，同时定义了类对象的存储与读取方案。
以下对CArchvie 的内部实现作分析。
CArchive使用了缓冲区，即一段内存空间作为临时数据存储地，对CArchive的读写都先依次排列到此缓冲区，当缓冲区满或用户要求时，将此段整理后的数据读写到指定的存储煤质。
当建立CArchive对象时，应指定其模式是用于缓冲区读，还是用于缓冲区写。
可以这样理解，CArchive对象相当于铁路的货运练调度站，零散的货物被收集，当总量到达火车运量的时候，由火车装运走。
当接到火车的货物时，则货物由被分散到各自的货主。与货运不同的是，交货、取货是按时间循序执行的，而不是凭票据。因此必须保证送货的和取货的货主按同样的循序去存或取。
对于大型的货物，则是拆散成火车单位，运走，取货时，依次取各部分，组装成原物。
缓冲区指针 BYTE* m_lpBufStart,指向缓冲区，这个缓冲区有可能是底层CFile(如派生类CMemFile)对象提供的，但一般是CArchive自己建立的。
缓冲区尾部指针 BYTE* m_lpBufMax;
缓冲区当前位置指针 BYTE* m_lpBufCur;
初始化时，如果是读模式,当前位置在尾部，如果是写模式，当前位置在头部:
m_lpBufCur = (IsLoading()) ? m_lpBufMax : m_lpBufStart;
对于基本的数据类型，例如字节、双字等，可以直接使用">>"、"<<"符号进行读出、写入。
//操作符定义捕: //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);
下面以双字为例，分析原码
双字的插入(写)
CArchive& CArchive::operator<<(DWORD dw){ if (m_lpBufCur + sizeof(DWORD) > m_lpBufMax) //缓冲区空间不够 Flush(); //缓冲区内容提交到实际存储煤质。 if (!(m_nMode & bNoByteSwap)) _AfxByteSwap(dw, m_lpBufCur); //处理字节顺序 else *(DWORD*)m_lpBufCur = dw; //添入缓冲区 m_lpBufCur += sizeof(DWORD); //移动当前指针 return *this;}
双字的提取(读)
CArchive& CArchive::operator>>(DWORD& dw){ if (m_lpBufCur + sizeof(DWORD) > m_lpBufMax) //缓冲区要读完了 FillBuffer(sizeof(DWORD) - (UINT)(m_lpBufMax - m_lpBufCur)); //重新读入内容到缓冲区 dw = *(DWORD*)m_lpBufCur; //读取双字 m_lpBufCur += sizeof(DWORD); //移动当前位置指针 if (!(m_nMode & bNoByteSwap)) _AfxByteSwap(dw, (BYTE*)&dw); //处理字节顺序 return *this;}
以上操作中，当缓冲区将插入满或缓冲区将提取空时，都将对缓冲区进行更新处理
缓冲区将插入致满时调用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 //写模式 { if (!m_bDirectBuffer) { // 内容写入到文件 if (m_lpBufCur != m_lpBufStart) m_pFile-> Write(m_lpBufStart, m_lpBufCur - m_lpBufStart); } else { //如果是直接针对内存区域的的(例如CMemFile中) (只需移动相关指针，指向新的一块内存) 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; //指向缓冲区首 }}
缓冲区将提取空将调用GFileeBuffer,nBytesNeeded为当前剩余部分上尚有用的字节
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; // 从文件中读取 if (!m_bDirectBuffer) { ASSERT(m_lpBufCur != NULL); ASSERT(m_lpBufStart != NULL); ASSERT(m_lpBufMax != NULL); if (m_lpBufCur > m_lpBufStart) { //保留剩余的尚未处理的部分，将它们移动到头 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 { // 如果是针对内存区域(CMemFile),移动相关指针，指向新的一块内存 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);}
以下分析
UINT Read(void* lpBuf, UINT nMax); 读取长度为nMax的数据
void Write(const void* lpBuf, UINT nMax); 写入指定长度nMax的数据
对于大段数据的读写，先使用当前缓冲区中的内容或空间读取或写入，若这些空间够用了，则结束。
否则，从剩余的数据中找出最大的缓冲区整数倍大小的一块数据，直接读写到存储煤质(不反复使用缓冲区)。
剩余的余数部分，再使用缓冲区读写。
(说明:缓冲区读写的主要目的是将零散的数据以缓冲区大小为尺度来处理。对于大型数据，其中间的部分，不是零散的数据，使用缓冲区已经没有意思，故直接读写)
①读取
UINT CArchive::Read(void* lpBuf, UINT nMax){ ASSERT_VALID(m_pFile); if (nMax == 0) return 0; UINT nMaxTemp = nMax; //还需要读入的长度，读入一部分，就减相应数值，直到此数值变为零 //处理当前缓冲区中剩余部分。 //如果要求读入字节小于缓冲区中剩余部分,则第一部分为要求读入的字节数， //否则读入全部剩余部分 UINT nTemp = min(nMaxTemp, (UINT)(m_lpBufMax - m_lpBufCur)); memcpy(lpBuf, m_lpBufCur, nTemp); m_lpBufCur += nTemp; lpBuf = (BYTE*)lpBuf + nTemp; //移动读出内容所在区域的指针 nMaxTemp -= nTemp; //当前缓冲区中剩余部分不够要求读入的长度。 //还有字节需要读，则需要根据需要执行若干次填充缓冲区，读出，直到读出指定字节。 if (nMaxTemp != 0) { //计算出去除尾数部分的字节大小(整数个缓冲区大小) //对于这些部分，字节从文件对象中读出，放到输出缓冲区 nTemp = nMaxTemp - (nMaxTemp % m_nBufSize); UINT nRead = 0; UINT nLeft = nTemp; UINT nBytes; do { nBytes = m_pFile-> Read(lpBuf, nLeft); //要求读入此整数缓冲区部分大小 lpBuf = (BYTE*)lpBuf + nBytes; nRead += nBytes; nLeft -= nBytes; } while ((nBytes > 0) && (nLeft > 0)); 知道读入了预定大小，或到达文件尾 nMaxTemp -= nRead; if (nRead == nTemp) //读入的字节等于读入的整数倍部分 该读最后的余数部分了 { // 建立装有此最后余数部分的内容的CArchive的工作缓冲区。 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); //从文件中读入到CArchive缓冲区 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; } //读出此剩余部分到输出 nTemp = min(nMaxTemp, (UINT)(m_lpBufMax - m_lpBufCur)); memcpy(lpBuf, m_lpBufCur, nTemp); m_lpBufCur += nTemp; nMaxTemp -= nTemp; } } return nMax - nMaxTemp;}
②保存,写入
void CArchive::Write(const void* lpBuf, UINT nMax){ if (nMax == 0) return; //读入可能的部分到缓冲区当前的剩余部分 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) //还有未写入的部分 { Flush(); //将当前缓冲区写入到存储煤质 //计算出整数倍缓冲区大小的字节数 nTemp = nMax - (nMax % m_nBufSize); m_pFile-> Write(lpBuf, nTemp); //直接写到文件 lpBuf = (BYTE*)lpBuf + nTemp; nMax -= nTemp; //剩余部分添加到缓冲区 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; }}
①CArchive提供的WriteString和ReadString
字符串写
void CArchive::WriteString(LPCTSTR lpsz){ ASSERT(AfxIsValidString(lpsz)); Write(lpsz, lstrlen(lpsz) * sizeof(TCHAR)); //调用Write，将字符串对应的一段数据写入}
字符串读(读取一行字符串)
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; //读出一个字节 // stop and end-of-line (trailing '\n' is ignored) 遇换行—回车 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对象,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对象的"<<"与">>"符读写字符串
CString定义了输入输出符,可以象基本类型的数据一样使用CArchive
的操作符定义
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, TCHARsCArchive& 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 archiveAFX_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;}
MFC中多数类都从CObject类派生，CObject类与CArchive类有着良好的合作关系，能实现将对象序列化储存到文件或其他媒介中去，或者读取预先储存的对象，动态建立对象等功能。
①CObject定义了针对CArvhive的输入输出操作符,可以向其他基本数据类型一样使用"<<"、"<<"符号
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; }
当使用这些符号时，实际上执行的是CArchive的WriteObject和ReadObject成员
②WriteObject与ReadObject
在WriteObject与ReadObject中先写入或读取运行时类信息(CRuntimeClas)，再调用Serialze(..),按其中的代码读写具体的对象数据。
因此，只要在CObject派生类中重载Serilize()函数，写入具体的读写过程，就可以使对象具有存储与创建能力。
//将对象写入到缓冲区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); //写入运行类信息 // enter in stored object table, checking for overflow CheckCount(); (*m_pStoreMap)[(void*)pOb] = (void*)m_nMapCount++; // 调用CObject的Serialize成员，按其中的代码写入类中数据。 ((CObject*)pOb)-> Serialize(*this); }}
CObject* CArchive::ReadObject(const CRuntimeClass* pClassRefRequested){ // attempt to load next stream as CRuntimeClass UINT nSchema; DWORD obTag; //先读入运行时类信息 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 { // 建立对象 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); //调用CObject的Serialize,按其中代码读入对象数据。 m_nObjectSchema = nSchemaSave; ASSERT_VALID(pOb); } return pOb;}
③运行时类信息的读写
为了避免众多重复的同类对象写入重复的类信息，CArchive中使用CMap对象储存和检索类信息。
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;}