C++ getline 后返回到文件开头
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Returning to beginning of file after getline
提问by bq54
So i've read all the lines from a file thusly
所以我已经从文件中读取了所有行
while (getline(ifile,line))
{
// logic
}
Where ifile is an ifstream and line is a string
其中 ifile 是一个 ifstream 而 line 是一个字符串
My problem is I now want to use getline over again, and seem to be unable to return to the beginning of the file, as running
我的问题是我现在想再次使用getline，并且似乎无法返回到文件的开头，因为正在运行
cout << getline(ifile,line);
Will return 0
将返回 0
I've attempted to use:
我尝试使用：
ifile.seekg (0, ios::beg);
To no avail, it seems to have no effect. How do I go back to the start of the file?
无济于事，似乎没有效果。我如何回到文件的开头？
回答by Konrad Rudolph
As of C++11, your seekgworks as expected, and you don't need to change anything.
从 C++11 开始，您seekg按预期工作，无需更改任何内容。
Before C++11:
在 C++11 之前：
Since you have reached the end of the file, the eofflag will be set. You need to clear that using ifile.clear– thentry seeking:
由于您已到达文件末尾，因此eof将设置标志。您需要清除使用ifile.clear–然后尝试寻找：
ifile.clear();
ifile.seekg(0, ios::beg);
回答by Angus Comber
This is because the eof flag has been set on the stream - due to you reaching the end of the file. so you have to clear this as an additional step.
这是因为已经在流上设置了 eof 标志 - 由于您到达了文件的末尾。所以你必须清除它作为一个额外的步骤。
Eg
例如
ifile.clear();
ifile.seekg (0, ios::beg);
回答by iko79
FYI: In my case, the order DID matter, thus
仅供参考：就我而言，订单确实很重要，因此
- clear
- seek
- 清除
- 寻找
otherwise the next getline operation failed (MSVC v120)
否则下一个 getline 操作失败 (MSVC v120)
