在 C++ 中重置 ifstream 对象的文件结束状态
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原文地址: http://stackoverflow.com/questions/7681555/
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Resetting the End of file state of a ifstream object in C++
提问by Steffan Harris
I was wondering if there was a way to reset the eof state in C++?
我想知道是否有办法在 C++ 中重置 eof 状态？
回答by Kerrek SB
For a file, you can just seek to any position. For example, to rewind to the beginning:
对于文件，您可以只查找任何位置。例如，要倒回开头：
std::ifstream infile("hello.txt");
while (infile.read(...)) { /*...*/ } // etc etc
infile.clear(); // clear fail and eof bits
infile.seekg(0, std::ios::beg); // back to the start!
If you already read past the end, you have to reset the error flags with clear()as @Jerry Coffin suggests.
如果你已经读到最后，你必须clear()按照@Jerry Coffin 的建议重置错误标志。
回答by Jerry Coffin
Presumably you mean on an iostream. In this case, the stream's clear()should do the job.
大概你的意思是在 iostream 上。在这种情况下，流clear()应该完成这项工作。
回答by user3176017
I agree with the answer above, but ran into this same issue tonight. So I thought I would post some code that's a bit more tutorial and shows the stream position at each step of the process. I probably should have checked here...BEFORE...I spent an hour figuring this out on my own.
我同意上面的答案，但今晚遇到了同样的问题。所以我想我会发布一些更多教程的代码，并在流程的每一步显示流位置。我可能应该在这里检查......之前......我花了一个小时自己解决这个问题。
ifstream ifs("alpha.dat"); //open a file
if(!ifs) throw runtime_error("unable to open table file");
while(getline(ifs, line)){
//......///
}
//reset the stream for another pass
int pos = ifs.tellg();
cout<<"pos is: "<<pos<<endl; //pos is: -1 tellg() failed because the stream failed
ifs.clear();
pos = ifs.tellg();
cout<<"pos is: "<<pos<<endl; //pos is: 7742'ish (aka the end of the file)
ifs.seekg(0);
pos = ifs.tellg();
cout<<"pos is: "<<pos<<endl; //pos is: 0 and ready for action
//stream is ready for another pass
while(getline(ifs, line) { //...// }
