C# structure size evaluation

Question

Please, can anyone tell what is the size of the structure, and how to calculate it:

[StructLayoutAttribute(LayoutKind.Sequential, Pack=2)]
public struct SomeStruct
{
     public short sh;
     public int   i;
     public byte  b;
     public ushort u;
     [MarshalAs(UnmanagedType.ByValArray, SizeConst=7)]
     public byte[] arr;
}

Should be 118 bytes. To be sure, the easist way is to make a small console program with Console.WriteLine(sizeof(SomeStruct)). — Thomas Weller, Dec 21 '13 at 15:58

Felice Pollano · Accepted Answer · 2013-12-22T18:00:55.270

I suppose you want to understand how is memory allocated, otherwise you can use:

System.Runtime.InteropServices.Marshal.SizeOf(TheStruct)

Well you choose to pack in a 2 byte boundary, so you basically allocate memory at step of two. so short ( signed or unsigned ) take 2 bytes, int take four bytes byte would take just one, but due to the packing you specify take two as well, for the same reason for the array we need to consider 8. So we have

2+4+2+2+8 = 18 bytes

score 1 · Answer 2 · answered Dec 21 '13 at 15:57

1

You can get exact size of this structure using following code -

System.Runtime.InteropServices.Marshal.SizeOf(SomeStruct)

answered Dec 21 '13 at 15:57

Bhalchandra K

2,631
3
31
43

score 0 · Answer 3 · edited May 23 '17 at 11:50

0

Try this:

int size = System.Runtime.InteropServices.Marshal.SizeOf(new SomeStruct());
Console.WriteLine(size);

or, from a related post, this:

int size;
unsafe
{
    size = sizeof(SomeStruct);
}

Both will yield 18, as Felice Pollano has explained.

edited May 23 '17 at 11:50

Community

1
1

answered Dec 21 '13 at 16:08

Igor Ševo

5,459
3
35
80

C# structure size evaluation

3 Answers3