Question

I am trying to find the number of times the code has been executed using the code below. But it doesn’t work.

#include <iostream>
#include <fstream>
#include <conio.h>

using namespace std;

int main()
{ 
    fstream outputFile;
    outputFile.open("count.txt");

    int count;
    outputFile>>count;
    count = count + 1;
    cout<<count;
    outputFile <<count << endl;
    outputFile.close();
    getch();
    return 0;
}

What could be the issue?

Answer 1

I recommend separating the concerns of (1) reading the file, (2) manipulating the data and (3) updating the file.

You should also introduce some error-handling and initialise your variables.

Here is some code to get you started:

#include <iostream>
#include <fstream>

int main()
{
    using namespace std;

    const char filename[] = "count.txt";
    int count = 0;

    {
        ifstream inputFile(filename);

        if (!(inputFile >> count))
        {
            cerr << "An error occurred while reading the persisted count" << endl;
        }
    }

    ++count;

    cout << count;

    {
        ofstream outputFile(filename);
        if (!(outputFile << count << endl))
        {
            cerr << "An error occurred while writing the persisted count" << endl;
        }
    }
}

But this is not finished. Each of the concerns I mentioned above should be extracted into separate functions.

And then you have to consider thread-safety. This would be easy enough using locking.

But what happens when you execute multiple instances of your application at the same time? You’ll need to do some file-based locking for this.

If you want to count executions on multiple machines, you have an even more interesting problem to solve.