What is the significance of using checked here

Question

Can anyone elaborate following statement:

byte[] buffer = new Byte[checked((uint)Math.Min(32 * 1024, (int)objFileStream.Length))];  

why i should not use

byte[] buffer = new Byte[32 * 1024];  

Answer 1

Attempt was to throw exception if objFileStream.Length will return number greater then int.MaxValue (2147483647), because Length on Stream returns long type (I assume objFileStream is stream). In .net arithmetic overflow is not checked by default.

Next code demonstrates this case:

long streamLength = long.MaxValue; //suppose buffer length is big

var res = checked( (int)(streamLength + 1) ); //exception will be thrown

Console.WriteLine( res ); //will print 0 in you comment checked keyword 

After short analysis, you can reduce next statement

new Byte[checked((uint)Math.Min(32 * 1024, (int)objFileStream.Length))]; 

to

new Byte[Math.Min(32 * 1024, checked((int)objFileStream.Length))];

Personal recommendation: I don't see how OverflowException will help you here. Math.Min will ensuse, that array will be created no longer than 32768 items. If you try to catch somewhere in the calling method, you won't be able to deduce what is the reason of that error, it may come from anywhere in the called stack.

So you probably need not to always allocate array of size 32768 as you proposed

byte[] buffer = new Byte[32 * 1024]; 

but still use Math.Min so that you'll save storage, if objFileStream.Length will return small number

byte[] buffer = new Byte[Math.Min(32 * 1024, objFileStream.Length)];