How to convert C# struct to C struct?

Question

[StructLayout(LayoutKind.Sequential, Size = 280), Serializable]
public struct AESContext
{
    /// int nr; 
    [MarshalAsAttribute(UnmanagedType.I4, SizeConst = 4)]
    public int nr;

    /// unsigned long *rk;
    [MarshalAsAttribute(UnmanagedType.U4, SizeConst = 4)]
    public uint rk;

    // unsigned long buf[68];
    [MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst = 68)]
    public uint[] buf;
}

This is C# struct I have so far. Comment above each field is type in C. I would love if someone could verify.

Are you targeting Windows from C as well?

M.Babcock
– M.Babcock

2012-02-18 22:11:50 +00:00
Commented Feb 18, 2012 at 22:11 — M.Babcock
– M.Babcock, Commented Feb 18, 2012 at 22:11

JaredPar · Accepted Answer · 2012-02-18 22:14:20Z

6

It sounds like you're trying to get the C# struct for the C struct defined in the member contents. If so then I believe you want the following

[StructLayout(LayoutKind.Sequential), Serializable]
public struct AESContext
{
    /// int nr; 
    public int nr;

    /// unsigned long *rk;
    public UIntPtr rk;

    // unsigned long buf[68];
    [MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst = 68)]
    public uint[] buf;
}

Basic changes

Don't specify SizeConst in StructLayout unless you are trying to create a struct whose size is different (typically) bigger than it's contents. It's not very common to do this
MarshalAs isn't usually needed for primitive types
Use IntPtr or UIntPtr to PInvoke pointer types. They vary properly in size between 32 and 64 bit platforms

answered Feb 18, 2012 at 22:14

JaredPar

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