Returning to beginning of file after getline

So i've read all the lines from a file thusly

while (getline(ifile,line))
    {
        // logic
    }

Where ifile is an ifstream and line is a string

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

cout << getline(ifile,开发者_如何学Cline);

Will return 0

I've attempted to use:

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?

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Since you have reached (and attempted to read past) the end of the file, the eof and fail flags will be set. You need to clear them using ifile.clear – then try seeking:

ifile.clear();
ifile.seekg(0);

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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.

Eg

ifile.clear();
ifile.seekg (0, ios::beg);

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FYI: In my case, the order DID matter, thus

1. clear
2. seek

otherwise the next getline operation failed (MSVC v120)