Difference between array.GetLength(0) and array.GetUpperBound(0)

What is the difference between these two methods and when would you use one instead of the other?

int[,] array = new int[4,3];
int length0 = array.GetLength(0);
int upperbound0 = array.GetUpperBound开发者_开发技巧(0);

MSDN says that GetLength return the number of elements where as GetUpperBound determine the max index, but how could this be different since arrays are initialized with elements for each index?

Take a look at this (rarely used) method. From Docs:

public static Array CreateInstance(Type elementType, int[] lengths, int[] lowerBounds)

Creates a multidimensional Array of the specified Type and dimension lengths, with the specified lower bounds.

With it, you can create an array with indices from -5 ... +5. If you ever use this kind of array, then GetUpperBound() suddenly becomes a lot more useful than GetLength()-1. There also exists a GetLowerBound().

But the C# support for this kind of arrays is low, you cannot use []. You would only need those methods in combination with the Array.GetValue() and SetValue() methods.

Array.Length returns the length of the array (number of elements) you need to subtract 1 from it to get the UpperBound.

Array.GetUpperBound(0) returns the upper bound of the array, you can use it as is.

GetUpperBound returns the highest index in the array, the GetLength returns the number of elements of the array.

i.e. GetUpperBound = GetLength - 1

Generally, array.GetUpperBound(0) = array.Length - 1, but since we can create arrays that have a Nonzero lower bound, that is not always true.

I realise this is an old question but I think it's worth emphasising that GetUpperBound returns the upper boundary of the specified dimension. This is important for a multidimensional array as in that case the two functions are not equivalent.

// Given a simple two dimensional array
private static readonly int[,] USHolidays =
{
    { 1, 1 },
    { 7, 4 },
    { 12, 24 },
    { 12, 25 }
};

The Length property will output 8 as there are 8 elements in the array.

Console.WriteLine(USHolidays.Length);

However, the GetUpperBound() function will output 3 as the upper boundary of the first dimension is 3. In other words I can loop over array indexes 0, 1, 2 and 3.

Console.WriteLine(USHolidays.GetUpperBound(0));
for (var i = 0; i <= USHolidays.GetUpperBound(0); i++)
{
    Console.WriteLine("{0}, {1}", USHolidays[i, 0], USHolidays[i, 1]);
}

if lower bound of your array is 0 then you can use either of them without any confusion but i would recommend array.length-1 as it is widely used. however, if the lower bound of your array is less than 0 then you should use array.GetUpperBound(0) because in this case array.length-1 != array.getUpperBound(0)