Reading a log file which is currently writen by another application

unbear · #1 23-Feb-2009, 02:05

Hello,

I am trying to read a log file which is written by another application.

Other application is running,and writing lines to log file time to time.
At the same time I supposed to read log file without lose and as soon as modification occurs.

Even I check if the error occurs when opening file,
I can not get the line written when open file error occurs.
But it can not get some lines of the log file.

Below you can find the function which I am using to accomplish this job.

Thanks a lot

p.s. : I can not modify the other application.

CPP / C++ / C Code:

while(1) 
        { 
            loopTry++; 
            if(CFile::GetStatus(fileName,filestatus)) 
            { 
                if(filestatus.m_size > lastSize) 
                { 
                    if ( !myFile.Open( fileName, CFile::shareDenyWrite | //  
                    CFile::modeRead  , &fileException ) )  
                    { 
                        CString cs; cs.Format(_T("Can't open file %s, error = %u readTry = %d"), 
                        fileName, fileException.m_cause,readTry ); 
                        log(cs); 
 
                    } 
                    else//oku 
                    { 
                        readTry++; 
                        char * rBuffer = ::new char[filestatus.m_size+1-cursorPos]; 
                        rBuffer[filestatus.m_size-cursorPos] = '\0'; 
 
                        //READ START 
                        myFile.LockRange(0,filestatus.m_size);// 
                        myFile.Seek(cursorPos, CFile::begin);//TODO: compare seek overhead with reading up to cursorPos 
                        myFile.Read(rBuffer,filestatus.m_size-cursorPos); 
                        myFile.UnlockRange(0,filestatus.m_size); 
                        myFile.Close(); 
                        //READ END 
                        lastSize = filestatus.m_size; 
                        //PROCESS START 
                        std::string str(rBuffer); 
                        int lineEndPos = 0; 
                        int localCursor = 0; 
                        for(;;) 
                        { 
                        std::string line; 
                         
 
                        int lastNewlineIndex = str.find("\r\n",lineEndPos+1); 
                        if(lastNewlineIndex == std::string::npos)//if there is no newline left 
                        { 
                        break; 
                        } 
                        lineEndPos = lastNewlineIndex; 
                        line = str.substr(localCursor,lineEndPos-localCursor); 
                        ProcessLine(line,loopTry,readTry);// some func to process line read  
                        localCursor = lineEndPos + 2; 
                        cursorPos += localCursor; 
                        } 
                        //PROCESS END 
                        ::delete [] rBuffer; 
                    } 
                } 
                else//file size is not changed. wait                { 
                Sleep(wait); 
                } 
            } 
            else 
            { 
                CString cs; cs.Format(_T("can not get status. looptry = %d"),loopTry ); 
                log(cs); 
            }    
        }

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