Optimize class member layout needed? (Byte padding)

[Sypher2]

In Visual Basic .NET is it necessary to pay attention to the layout of member variables? I know in C++ the order in which you declare your variable can have an affect on the amount of RAM used. This is because of byte alignment and padding.

Example:

[blue]Dim[/blue] b [blue]As[/blue] Byte  [green]'1 byte[/green]
[blue]Dim[/blue] i [blue]As[/blue] Int32 [green]'4 bytes[/green]
[blue]Dim[/blue] s [blue]As[/blue] Int16 [green]'2 bytes[/green]

Usually variables are aligned in memory in 4 byte segments. In the above example the first variable "b" takes up 1 byte. Since the second variable "i" is 4 bytes, it cannot fit in the same block as "b". So "b" is padded with an additional 3 bytes. The last variable "s" is also padded with and addition 2 bytes.

Even though 8 total bytes are declared, the RAM usage is 12 bytes.

If you rearrange to:

[blue]Dim[/blue] i [blue]As[/blue] Int32 [green]'4 bytes[/green]
[blue]Dim[/blue] s [blue]As[/blue] Int16 [green]'2 bytes[/green]
[blue]Dim[/blue] b [blue]As[/blue] Byte  [green]'1 byte[/green]

"i" fits into one 4 byte segment. Since "s" and "b" are declared one after the other, you can fit them both into a segment...3 bytes total then 1 byte padding to complete the segment.

You now are using 8 bytes instead of 12.

Is this necessary in .NET?

 

[macleod1021]

hmmm...I have no idea. My first thought is that it shouldn't considering that .net is managed by the CLR; but I may be wrong