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;
}
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