C＃Marshal.SizeOf

Question

I am using Marshal.SizeOf to know the size of my stucture:

struct loginStruct
{
    public string userName;
    public string password;

    public loginStruct(string userName, string password)
    {
        this.userName = userName;
        this.password = password;
    }
}

Here is the use of this function:

int len = Marshal.SizeOf(typeof(loginStruct));

I got 2 programs. In one program len is equals to 8. In the other it equals to 16. It is the same struct. Why I got that differece?

Answer 1

我猜一个程序是针对AnyCPU（在64位平台上将是64位）和一个32位编译的。

Answer 2

Methods don't affect the size given, so effectively we're talking about:

struct loginStruct
{
    public string userName;
    public string password;
}

That struct has two reference type fields. As such, it has two fields in the memory which refer to objects on the heap, or to null .

All reference type fields are 4 bytes in 32-bit .NET and 8 bytes in 64-bit .NET.

Hence the size would be 4 + 4 = 8 in 32-bit .NET or 8 + 8 = 16 in 64-bit .NET.

Answer 3

It is depending on the machine and on the build configuration. As @Joey said AnyCPU or 64-Bit

There are some tricks to avoid this problem:

For example you can check:

• The application type Environment.Is64BitOperatingSystem

• The size of IntPtr changes on 32 and 64

• using System.Runtime.InteropServices.Marshal.SizeOf(typeof(Win32DeviceMgmt.SP_DEVINFO_DATA)