二分查找返回负值

Question

I have a list of Series and a vertical annotation. I want to have the Y value of the signals for every X position of the vertical annotation (VA).

Here is what I have done so far.

VerticalAnnotation VA;                
List<double> Points = new List<double>();

foreach (var sig in Signals)
{
    for (int g = 0; g < sig.Points.Count; g++)
    {
        Points.Add(sig.Points[g].XValue);
    }
    Points.Sort();
}

and

private void chart1_AnnotationPositionChanging(object sender, AnnotationPositionChangingEventArgs e)
{
    var x = Points.BinarySearch(VA.X);
}

But for some reason x variable gets negative values which does not make sense.

Answer 1

The docs say this:

Returns ... the zero-based index of item in the sorted List, if item is found; otherwise, a negative number that is the bitwise complement of the index of the next element that is larger than item or, if there is no larger element, the bitwise complement of Count

Note that the latter value is also negative.

A negative result means that what you are looking for is not in the list. Also the result can be used (by inverting it as ~result ) to know where the value at hand would have been found if it had been in the list, or where you would need to insert it to keep the list nicely sorted.