线程读取文件的问题
#include "windows.h "
#include <utility>
#include <string>
#include <fstream>
#include <iostream>
using namespace std;
//#include <ansi_c.h>


DWORD id;
HANDLE ch;

int chechen;

void Check_Time(void);


SYSTEMTIME ti;

/*
typedef struct _SYSTEMTIME {
WORD wYear;
WORD wMonth;
WORD wDayOfWeek;
WORD wDay;
WORD wHour;
WORD wMinute;
WORD wSecond;
WORD wMilliseconds;
} SYSTEMTIME, *PSYSTEMTIME;
*/


void main(void)
{
chechen = 0;
ch = CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)Check_Time,0,0,&id);
WaitForSingleObject(ch, INFINITE);
}
void Check_Time(void)
{
char *tim, time[100];
int i;

/////////////////////////////////////////////////////////////////////////////
char * file= "C:\\Program Files\\Gene6 FTP Server\\Log\\emma-transfers.log ";
ifstream ifs;
ifs.open(file,ios::binary);//open file the file name can be replaced
ifs.seekg (0, ios::end);
int dwFilePosition=ifs.tellg();
int length=0;
ifs.seekg(0,ios::beg);
string str;
ifs.close();
char buf[1024];


//////////////////////////////////////////////////////////////////////////////

while (1)
{
Sleep(5000);

ifs.open( "C:\\Program Files\\Gene6 FTP Server\\Log\\emma-transfers.log ",ios::binary);//open file the file name can be replaced
ifs.seekg(0,ios::end);
length=ifs.tellg();
ifs.seekg(0,ios::beg);
int newadded=length-dwFilePosition;
cout < < "length: " < <length < <endl;
ifs.seekg (-newadded, ios::end); //added newadded bytes




if (length <dwFilePosition)
{
ifs.getline(buf,100, '\n ');
cout < <buf < < "no changed " < <endl;
cout < <length < < " this is length " < <endl;
cout < <dwFilePosition < < " position " < <endl;
//The file has rolled over... (or it 's been cleared)


}
else if(length==dwFilePosition)
{}

else if(length> dwFilePosition)
{
memset(buf,0,1024);
ifs.getline(buf,100, '\n ');

//ifs.getline(buf,100, '\n ');
cout < <buf < < "changed " < <endl;
///if the file has been changed, it should notify the program to print the
//newly added lines
//and continue

cout < <length < < " this is length " < <endl;

cout < <dwFilePosition < < " position " < <endl;
dwFilePosition=length;
}
ifs.close();

}
}


下面是输出结果：
length: 10742
length: 10742
length: 10742
length: 10742
length: 10742
length: 10742
length: 10742
length: 10861
07/02/08 15:12:05, 10, 127.0.0.1, liuxiaoyun, STOR E:\ftphome\sn.txt from 0 to 1
24 in 00:00:01 at 0changed
10861 this is length
10742 position
length: -1
no changed
-1 this is length
10861 position
length: -1
no changed
-1 this is length
10861 position
length: -1


为什么下面的length在文件长度改变后变成了-1呢？

[解决办法]
帮顶
[解决办法]
basic_istream::getline "The function extracts up to _Count - 1 elements and stores them in the array beginning at _Str "

You can get ride of this problem by adding following after "ifs.getline(buf,100, '\n ') "

if (ifs.fail()) ifs.clear();