CODEWITHSUNDEEP
c#arraysbounds
LaserProject
LaserProject

Reputation: 25

How to specify the bounds of an array

There i try to specify bounds of an array:

public string[] scaleChanged()
{
    int j =0;
    for(int i=0;i<42;i++)
    {
        if(MinScale == ItemScale[i]) //MinScale is the min value I want to use to start array
        {
            ItemsScale[j] = MinScale; //ItemScal is an array of 42 string
            for(int h =0; h<42-i; h++)
            {
                ItemScale[j+1] = ItemScale[i];
                j++;
                if(ItemScale[j] == MaxScale) //MaxScale is my max value I want to use for stop my array
                {
                    return ItemScale[ ???MinScale to MaxScale];
                }
            }
        }
    }
}

So I recover 2 value from a server which allow me to specify bounds of my array.

So I try to define a new array with this two values as bounds.I precise this "two values" are always declared anywhere in my ItemScale array (that is why i use comparaison).

Upvotes: 1

Views: 1125

Answers (1)

Marc Gravell
Marc Gravell

Reputation: 1062780

If really depends what you are trying to do here. The bounds of an array are fixed at creation, and in the case of a vector (string[] is a vector), it is always zero-based. If you want an actual array, then you'll need to copy out the sub-range into a second array - just new the array of the correct size, and Array.Copy the element range you want - i.e. Array.Copy(source, startIndex, destination, 0, count);. However, there are ways to represent a range without copying:

  • if the receiver just needs to iterate the data (rather than access it by index), an IEnumerable<T> - i.e. return source.Skip(firstIndex).Take(count);
  • Span<T> or ReadOnlySpan<T>, i.e. return new Span<string>(source, firstIndex, count) - a "span" works much like an array, and doesn't require any copying, and is allocation-free; the offset etc is applied appropriately; note that once you have a span, .Slice(...) creates smaller and smaller sub-sections inside that span, again without any copying or allocations
    • one nice thing here is that you can use the span approach as a simpler way of dealing with creating a new array if you want - once you have a [ReadOnly]Span<T>, you can use .ToArray() to create a new array with those contents
  • Memory<T> or ReadOnlyMemory<T> is effectively "I can give you a span when you want one" - because you can't store a "span" as a field (it is only legal on the stack), but you can store a "memory"
  • ArraySegment<T> is an older metaphor for expressing an array with offset and count; it relies on the caller doing everything correctly

Upvotes: 3

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