该循环执行的迭代次数超出预期

Question

I am having problems with the following code. What I expect is for the do-while loop to execute 4 times, once for each line of the text file it is reading in, but in reality is it executing five time, which is resulting in a segfault later in the program. What am I doing wrong here that's causing it to execute the extra iteration? I've tried replacing he do-while with a simple while loop but the result is the same.

int count = 0;
string devices[4];
string line;
ifstream DeviceList;
DeviceList.open("devices/device_list.txt");
do
{
 getline(DeviceList, line);
 devices[count] = line;
 count ++;
} while(!DeviceList.eof());

device_list.txt contains the following:

WirelessAdaptor
GPU
CPU
Display

Answer 1

I think your loop should probably look more like this:

Edit: Added check to ignore empty lines

while (getline(DeviceList, line))
{
    if (line.length() > 0)
    {
        devices[count] = line;
        ++count;
    }
}

Answer 2

除非您尝试读取的数据多于剩余数据，否则eof（）不会返回true。

Answer 3

eof() doesn't return true until getline consumes the end. It doesn't do this until the getline call after reading the last line. You need to check if eof is true immediately after your getline call:

while(true)
{
  getline(DeviceList, line);
  if(DeviceList.eof())
    break;
}

Answer 4

Above the line getline(DeviceList, line); insert cout << line.length() << endl; and tell us what happens.

Answer 5

您的文本文件可能在最后一行之后包含换行符，因此getline在循环实际结束之前读取一个空字符串。