C#中结构体指针到底怎么用啊？

Question

struct SLPCI 
        {
            byte StartChar;
            byte Length;
            byte ControlArear;
        }
 SLPCI* LPCIHead; char[] sendbuf = new char[300]; LPCIHead = (SLPCI*)sendbuf;
LPCIHead->StartChar=68h;我想把初始化了的结构体存到数组sendbuf中，
这样写为什么不对啊？

Answer 1

    struct SLPCI
    {
        public byte StartChar;
        public byte Length;
        public byte ControlArear;        public SLPCI(byte i, byte j, byte k)
        {
            StartChar = i;
            Length = j;
            ControlArear = k;
        }
    } 
            int len = Marshal.SizeOf(typeof(SLPCI));
            SLPCI slp = new SLPCI(1,2,3);
            byte[] sendbuf = new byte[len];
            IntPtr ptr = Marshal.AllocHGlobal(len);
            Marshal.StructureToPtr(slp, ptr, true);
            Marshal.Copy(ptr, sendbuf, 0, len);
            Marshal.FreeHGlobal(ptr);

Answer 2

            char[] buf = new char[300];
            unsafe
            {
            //char * buf=stackalloc char[300];
                
                fixed (char* pbuf = buf)
                {
                    MyStruct* PStructDemo = (MyStruct*) pbuf;
                    PStructDemo->i = 1;
                    PStructDemo->j = 2;
                    PStructDemo->k = 3;
                }
            }