Question

I’m trying to create a word sorting program that will read the words in a .txt file and then write them to a new file in order from shortest words to longest words. So, for instance, if the first file contains:

elephant

dog

mouse

Once the program has executed, I want the second file (which is initially blank) to contain:

dog

mouse

elephant

Here’s the code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    string word;
    ifstream readFrom;
    ofstream writeTo;
    readFrom.open("C:\\Users\\owner\\Desktop\\wordlist.txt");
    writeTo.open("C:\\Users\\owner\\Desktop\\newwordlist.txt");
    if (readFrom && writeTo)
    {
        cout << "Both files opened successfully.";
        for (int lettercount = 1; lettercount < 20; lettercount++)
        {
            while (readFrom >> word)
            {
                if (word.length() == lettercount)
                    { 
                        cout << "Writing " << word << " to file\n";
                        writeTo << word << endl;
                    }
            }
            readFrom.seekg(0, ios::beg); //resets read pos to beginning of file
        }
    }
    else
        cout << "Could not open one or both of files.";

    return 0;
}

For the first iteration of the for loop, the nested while loop seems to work just fine, writing the correct values to the second file. However, something goes wrong in all the next iterations of the for loop, because no further words are written to the file. Why is that?

Thank you so much.

Answer 1

while (readFrom >> word)
{

}
readFrom.seekg(0, ios::beg); //resets read pos to begin

The while loop will continue until special flags are set on readFrom, namely, the EOF flag. Seeking to the beginning does not clear any flags, including EOF. Add the following line right before the seek to clear the flags and your code should work fine.

readFrom.clear();