CODEWITHSUNDEEP
c#c++.netpinvoke
nishantcop
nishantcop

Reputation: 1017

Marshal.SizeOf(strurtureType) Always throws error

Following is my code snippet 

class Program
{
    static void Main(string[] args)
    {
        Program.GetState(new State() { enabled = true, currentLimit = 30 });
    }

    private static void GetState(State result)
    {
        IntPtr Ptr = Marshal.AllocHGlobal(Marshal.SizeOf(result));
        Marshal.StructureToPtr(result, Ptr, false);
    }
}

[StructLayout(LayoutKind.Sequential)]
public struct State
{
    [MarshalAsAttribute(UnmanagedType.I8)]
    public uint currentLimit;
    [MarshalAsAttribute(UnmanagedType.I1)]
    public bool enabled;
}

It always throws an error i.e.

Type 'MarshellingStructureSize.State' cannot be marshaled as an unmanaged structure; no meaningful size or offset can be computed.

My intention is to send a structure for a native DLL through pInvoke but when I try to allocate memory for my structure in Managed code through Marshal it always throw above error.

Any help would be greatly appreciated.

Upvotes: 0

Views: 2135

Answers (1)

Sriram Sakthivel
Sriram Sakthivel

Reputation: 73472

uint is actually alias for System.UInt32 which occupies 4 bytes in memory. I think currentLimit can't be converted to 8 bytes in memory, that is why you get an error.

[MarshalAsAttribute(UnmanagedType.I8)]
public uint currentLimit;

I8 is for signed 8 byte integer. try changing it to U4 or I4. 

[MarshalAsAttribute(UnmanagedType.U4)]
public uint currentLimit;

Or change type of currentLimit to ulong as @Hans Passant suggested.

[MarshalAsAttribute(UnmanagedType.I8)] //or U8 
public ulong currentLimit;

this works.

Upvotes: 2

Related Questions