Can't iterate feature in while nested iteration

Question

I need to do some operation with every combinations of features in two FeatureClasses. The "for" iterating operator is very very slow-working, so I decided to try "while" operator and using FeatureCursor. So nested iteration I have like below:

    IFeatureCursor fcur1 = fc1.Search(null, false);
    IFeatureCursor fcur2 = fc2.Search(null, false);

    IFeature f1 = fcur1.NextFeature();
    IFeature f2 = fcur2.NextFeature();

        while (f1 != null)
        {
            //external cycle code
            MessageBox.Show("external cycle FID " + f1.Value[0].ToString());

            while (f2 != null)
            {
                //internal cycle code
                MessageBox.Show("internal cycle FID " + f1.Value[0].ToString());
                f2 = fcur2.NextFeature();
            }
            f1 = fcur1.NextFeature();
        }

For example, there are 3 features in each FeatureClass fc1 and fc2.

I use a MessageBoxes to show FID of feature f1 to understand what happens in external and internal iterations.

The expected order of MessageBoxes is:

external cycle FID 0
 internal cycle FID 0
 internal cycle FID 0
 internal cycle FID 0
external cycle FID 1
 internal cycle FID 1
 internal cycle FID 1
 internal cycle FID 1
external cycle FID 2
 internal cycle FID 2
 internal cycle FID 2
 internal cycle FID 2

But result of my code is:

external cycle FID 0
 internal cycle FID 0
 internal cycle FID 0
 internal cycle FID 0
external cycle FID 1
external cycle FID 2

So, external cycle operates with every feature f1, but internal cycle gets the first feature f1 only. Why another features f1 doesn't go to internal cycle?

Answer 1

You need to reset the the feature cursor after going through each iteration. See my edits:

IFeatureCursor fcur1 = fc1.Search(null, false);
IFeatureCursor fcur2;

IFeature f1; 
IFeature f2;

    while ((f1 = fcur1.NextFeature()) != null)
    {
        //external cycle code
        MessageBox.Show("external cycle FID " + f1.Value[0].ToString());

        fcur2 = fc2.Search(null, false);
        while ((f2 = fcur2.NextFeature()) != null)
        {
            //internal cycle code
            MessageBox.Show("internal cycle FID " + f1.Value[0].ToString());
        }
    }

You may also want to release the second cursor after iterating through its features.