部分載自：http://www.tongyi.net/develop/mfc/1003840.html
CArchive類是使用了緩沖區(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)。
一般來(lái)說(shuō)，CArchive封裝了對(duì)該緩沖區(qū)的操作，它的好處是可以少劃動(dòng)硬盤以及提高運(yùn)行速度。不過(guò)對(duì)于使用MFC來(lái)說(shuō)，是一個(gè)很好的封裝。看看其對(duì)讀寫的操作，可見(jiàn)在實(shí)際編程上是非常容易出錯(cuò)的。對(duì)于這樣的類，一定要封裝好，作為一個(gè)公用函數(shù)或公用類調(diào)用，否則在實(shí)際中像c那樣散在代碼的各個(gè)地方的話，恐怕有時(shí)頭會(huì)大。
有時(shí)我想，如果編程在這些地方磨洋工的話，恐怕一個(gè)大的工程軟件寫起來(lái)得好長(zhǎng)時(shí)間。所以說(shuō)盡量已組件的方式，類的思路來(lái)組合前人的算法，技巧也是一種編程的進(jìn)步。
所下列看其對(duì)指針的嫻熟操作（也是往往出錯(cuò)的啊），
例如雙字的插入(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;
}
內(nèi)部指針
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)，讀模式,當(dāng)前位置在尾部，是寫模式，當(dāng)前位置在頭部:
m_lpBufCur = (IsLoading()) ? m_lpBufMax : m_lpBufStart;
這里粘貼一個(gè)日志文件的類文件中使用CArchive作為內(nèi)部操作的例子吧。利用CArchive去Flush，Write，Open，這里先把CArchive的參量列出：
CArchive(CFile* pFile, UINT nMode, int nBufSize = 4096, void* lpBuf = NULL);
class CLogFile
{
protected:
int m_nCachBuffSize;
int m_nCurentBuffSize;
char * m_lpCachBuff;
CString m_fileName;
CArchive *m_pArchive; //作為文件讀寫到內(nèi)存的實(shí)際操作。
CFile m_file;
CRITICAL_SECTION m_csFile;
SYSTEMTIME m_tmCurTime; //當(dāng)前時(shí)間
SYSTEMTIME m_tmLastTime; //上次日志時(shí)間
public:
void Open(char *fileName);
void Close();
void Wirte(char * buff ,int size=0);
void WriteLog(char *szLog, int size =0);
void Flush();
CLogFile() ;
~CLogFile() ;
};
***************************************************
#include "stdafx.h"
#include "LogFile.h"
#include "pubfunc.h"
CLogFile :: CLogFile()
{
::InitializeCriticalSection(&m_csFile);
m_pArchive = NULL;
m_fileName = "";
m_lpCachBuff = new char[MAX_LOG_BUFF + 1 ]; //作為內(nèi)存緩沖區(qū)
m_nCachBuffSize = MAX_LOG_BUFF ;
m_nCurentBuffSize = 0;
}
CLogFile :: ~CLogFile()
{
if(m_pArchive)
{
m_pArchive->Flush();
m_file.Close();
delete m_pArchive;
m_pArchive= NULL;
}
if(m_lpCachBuff)
{
delete []m_lpCachBuff;
}
::DeleteCriticalSection(&m_csFile);
}
void CLogFile::WriteLog(char *szLog, int size)
{
if (size == 0)
size = strlen(szLog);
Wirte(szLog , size);
}
void CLogFile::Flush()
{
EnterCriticalSection(&m_csFile);
if(m_pArchive)
{
m_pArchive->Flush();
m_nCurentBuffSize=0;
}
LeaveCriticalSection(&m_csFile);
}
void CLogFile::Wirte(char * buff ,int size)
{
EnterCriticalSection(&m_csFile);
GetLocalTime(&m_tmCurTime);
char szTime[128]={0};
int timelen = sprintf(szTime,"\r\n%04d-%02d-%02d %02d:%02d:%02d\r\n\r\n",m_tmCurTime.wYear,m_tmCurTime.wMonth,m_tmCurTime.wDay,m_tmCurTime.wHour,m_tmCurTime.wMinute,m_tmCurTime.wSecond);
if (m_tmCurTime.wYear != m_tmLastTime.wYear
||m_tmCurTime.wMonth != m_tmLastTime.wMonth
||m_tmCurTime.wDay != m_tmLastTime.wDay)
{
if(m_pArchive)
{
m_pArchive->Flush();
m_file.Close();
}
char szFile[256],szPath[256];
GetLocalTime(&m_tmLastTime);
//GetAppPath(szPath);
szPath = "自己抓取當(dāng)前目錄吧，出錯(cuò)我不管了";
if(m_pArchive)
{
delete m_pArchive;
}
if(m_fileName.IsEmpty())
{
sprintf(szFile,"%s\\Log\\%d-%02d-%02d_%s.log",szPath,m_tmLastTime.wYear,m_tmLastTime.wMonth,m_tmLastTime.wDay,(LPTSTR)(LPCTSTR)m_fileName);
}else
{
sprintf(szFile,"%s\\Log\\%d-%02d-%02d.log",szPath,m_tmLastTime.wYear,m_tmLastTime.wMonth,m_tmLastTime.wDay);
}
if(m_file.Open(szFile,CFile::modeCreate|CFile::modeNoTruncate|CFile::modeReadWrite|CFile::shareDenyNone,0))
{
m_file.SeekToEnd();
m_pArchive = new CArchive(&m_file,CArchive::store,m_nCachBuffSize,m_lpCachBuff);
int totalsize = timelen + size ;
if( totalsize > ( m_nCachBuffSize - m_nCurentBuffSize) )
{
m_pArchive->Flush();
m_pArchive->Write( szTime ,timelen );
m_pArchive->Flush();
for ( int i =0 ; i < totalsize/m_nCachBuffSize;i++)
{
m_pArchive->Write(buff+m_nCachBuffSize * i ,m_nCachBuffSize);
m_pArchive->Flush();
}
m_nCurentBuffSize = totalsize - m_nCachBuffSize * (totalsize/m_nCachBuffSize);
m_pArchive->Write(buff+m_nCachBuffSize * (totalsize/m_nCachBuffSize) * i ,m_nCurentBuffSize);
m_lpCachBuff[m_nCurentBuffSize+1] = 0;
}
else
{
m_pArchive->Write( szTime ,timelen );
m_pArchive->Write( buff ,size );
m_nCurentBuffSize=m_nCurentBuffSize+ totalsize;
m_lpCachBuff[m_nCurentBuffSize+1]=0;
}
}
else
{
m_pArchive = NULL;
}
}
else
{//續(xù)寫log文件
if(m_pArchive)
{
int totalsize = timelen + size ;
if( totalsize > ( m_nCachBuffSize -m_nCurentBuffSize) )
{
m_pArchive->Flush();
m_pArchive->Write( szTime ,timelen );
m_pArchive->Flush();
for ( int i =0 ; i < totalsize/m_nCachBuffSize;i++)
{
m_pArchive->Write(buff+m_nCachBuffSize * i ,m_nCachBuffSize);
m_pArchive->Flush();
}
m_nCurentBuffSize = totalsize - m_nCachBuffSize * (totalsize/m_nCachBuffSize);
m_pArchive->Write(buff+m_nCachBuffSize * (totalsize/m_nCachBuffSize) * i ,m_nCurentBuffSize);
m_lpCachBuff[m_nCurentBuffSize + 1]=0;
}
else
{
m_pArchive->Write( szTime ,timelen );
m_pArchive->Write( buff, size );
m_nCurentBuffSize = m_nCurentBuffSize + totalsize;
m_lpCachBuff[m_nCurentBuffSize+1]=0;
}
}
}
LeaveCriticalSection(&m_csFile);
}
/*
fileName 文件名稱
*/
void CLogFile::Open( char *fileName)
{
m_nCurentBuffSize = 0;
::InitializeCriticalSection(&m_csFile);
char szFile[256],szPath[256];
GetLocalTime(&m_tmLastTime);
// GetAppPath(szPath);
szPath = "把szPath修改為類變量吧，然后找個(gè)獲取當(dāng)前目錄的函數(shù)，改動(dòng)下吧，白給你用這個(gè)類不看看也是不行的"
if(fileName == 0 || fileName[0] == 0)
{
sprintf(szFile,"%s\\Log\\%d-%02d-%02d.log",szPath,m_tmLastTime.wYear,m_tmLastTime.wMonth,m_tmLastTime.wDay);
}
else
{
m_fileName = fileName;
sprintf(szFile,"%s\\Log\\%d-%02d-%02d_%s.log",szPath,m_tmLastTime.wYear,m_tmLastTime.wMonth,m_tmLastTime.wDay,fileName);
}
if(m_file.Open(szFile,CFile::modeCreate | CFile::modeNoTruncate | CFile::modeReadWrite|CFile::shareDenyNone,0))
{
m_pArchive = new CArchive(&m_file,CArchive::store,m_nCachBuffSize, m_lpCachBuff);
}
else
{
m_pArchive = NULL;
}
}
void CLogFile::Close()
{
if(m_pArchive)
{
m_pArchive->Flush();
m_file.Close();
delete m_pArchive;
m_pArchive= NULL;
}
m_nCurentBuffSize = 0;
}