c++ - Why using while(!input.eof()) loop twice not working?

On the following lines of code is intended to put every words in the input text file(words are separated by new lines) to a vector of strings, then to turn each word inside out, and to see if this turned word is contained in the list of words in the input file.

I believe my binary search function and wordTurn function works fine.
I did several simple tests on my code, and I found out using while(!myFile.eof()) loop twice might be the cause for my code not working. By not working I mean I get the output file("pairs.txt") as an empty document(it is supposed to be a list of pairs of words).

That is, when I put some simple print code in the second while(!myFile.eof()) loop body, it did not get printed out, from which I concluded this loop is not reached. This is more likely, since it printed when I commented out the first while(!myFile.eof()) loop. I originally placed the first while loop at the else body, but this made no difference.

What do you think is the problem?
I tried combining those two loop body into the second loop, and it produces something in the output file, but this was not what this code was supposed to do, and this was logically not correct.

Any words of advice would be greatly appreciated.

int main(int argc, char* argv[]) {

    vector words;
    ifstream myFile(argv[1]);
    ofstream outputFile("pairs.txt");
    string vocab;
    string s;
    int count;


    while(!myFile.eof()) {                //first while(!myFile.eof()) loop
        getline(myFile, s);
        words.push_back(s);
    }

    if(argc != 2) {
        cout << "Usage: provide the name of one input file after the dictlookupHN executable file." << endl;
        return (1);
    }
    else {

        if(!myFile.is_open()) {
            cerr << "Error: unable to open file " << argv[1] << endl;
            return (1);
        }
        else {
            while(!myFile.eof()) {      //second while(!myFile.eof()) loop
                getline(myFile, vocab);
                string turnedWord = wordTurn(vocab);
                if(binsearch(words, turnedWord) != "") {
                    outputFile << vocab << ":" << turnedWord << endl;

                    count++;
                }
            }
        }

    }
    myFile.close();
    outputFile.close();

    return 0;

}

Answer

The ifstream class maintains an internal offset into the stream data, keeping track where it has to read from, for the next operation.

When this offset reaches the end, it stops the first loop, (eof() returns false). You need to reset this internal position back to the beginning of the file, before reading again.

You do that by saying:

myFile.clear(); // clear stream flags and error state

myFile.seekg(0, ios::beg); // reset read position

before the second loop.

Edit: Added call to clear().