Arrays

Question

1. Does c# Array size can be changed at runtime? For e.g. I start with a 10 member array of inegers and then later on at runtime if I insert a 11th integer - will it be possible?

C Kelvin · Answer

Thanks Vulpes.

Vulpes · Answer

That's right. Internally the ArrayList uses an array of objects as its backing store. If I remember correctly the initial size of the internal array is 4 but when a fifth element is added this is doubled to 8 and continues to be doubled as needed. However the difference between this and Array.Resize is that you don't have to think about it - it's done automatically for you in the background. List works in a similar fashion but is 'strongly typed' i.e. the internal array is of type T rather than object. In the case of value types (int double bool etc) this means that 'boxing' - a relatively slow operation - is not needed and when retrieving an element from the collection you don't have to cast it to its actual type.

C Kelvin · Answer

Thanks. So when you wrote>> if you're still using .NET 1.1) an ArrayList. These automatically increase their sizes as new elements are added. So as per example you have given: This will mean compiler internally again copies the old array and creates a new one with same name and discards the old one to adjust for the newly added array element that is beyond the upper boundary of the original array?

Vulpes · Answer

Well it's possible to resize an array. For example: int[] myArray = {1 2 3 4 5 6 7 8 9 10}; Array.Resize(ref myArray 11); myArray[10] = 11; However this actually creates a new array and copies the elements of the old array to the new one. It doesn't change the size of the original array which is technically impossible. If you need a resizeable collection then it's generally better to use a List or (if you're still using .NET 1.1) an ArrayList. These automatically increase their sizes as new elements are added.