Question

I’m just a beginner at c++ so I might be doing something wrong but anyways I created a c++ dll and I call it from my wpf project:

c++ code:

extern "C" __declspec (dllexport) double writeTxt()
{   
    ofstream mf("c:\\cpp.txt");     
    for(int i=0;i<999;i++)
    {
     mf<<"xLine: \n";
    }
    mf.close();
    return 1;

}

calling code from c#:

[DllImport(@"C:\Users\neo\Documents\visual studio 2010\Projects\TestDll\Debug\TestDll.dll",
       CallingConvention = CallingConvention.Cdecl)]
    public static extern double writeTxt();

Now I’m trying to compare the execution time with this c# function:

double writeTxtCs()
    {
        StreamWriter sw = new StreamWriter(@"c:\cs.txt");
        for (int i = 0; i < 999; i++)
        {
            sw.WriteLine("Line: " + i);
        }
        sw.Close();
        return 0;
    }

but the c# function is about twice as faster than the c++ function.
tested like this:

private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        long[] arr = new long[100];
        Stopwatch sw = new Stopwatch();
        for (int i = 0; i < 99; i++)
        {
            sw.Start();
            //double xxx = writeTxt();
            double xxx = writeTxtCs();
            arr[i] = sw.ElapsedMilliseconds;
            sw.Reset();
        }
        MessageBox.Show(arr.Average().ToString());
        Close();
    }

When running the c# function I normally get ~0.65ms and when running the c++ function I get ~1.1ms.
my question is: am I doing something wrong or does c# really is faster in this scenario than c++?

Answer 1

All other answers have valid points. In addition to those:

You are testing against “Debug” build of your C++ DLL and that might be degrading C++ performance more than how it affects C#’s performance. Try unleashing optimizations on both and see how it works out for you.

Nevertheless I/O doesn’t have much to do with the “language”. It’s more about runtime and the OS.