一.概述
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。
二.内部数据
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;
三.基本数据读写 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;
}
四.缓冲区的更新以上操作中，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,会调用FillBuffer。 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);
}
五.指定长度数据段落的读写以下分析
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;
}
}
六.字符串的读写
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, 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派生对象的读写 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;
}