I have union inside structure and the structure looks like

struct tDeviceProperty {

DWORD Tag;
DWORD Size;     
union _DP value;    

};

typedef union _DP { short int i;
LONG l;
ULONG ul;
float flt;
double dbl;
BOOL b;
double at;
FILETIME ft;
LPSTR lpszA;
LPWSTR lpszW;
LARGE_INTEGER li;
struct tBinary bin;
BYTE reserved[40]; } __UDP;

struct tBinary { ULONG size;
BYTE * bin;
};

from the tBinary structure bin has to be converted to tImage (structure is given below)

struct tImage { DWORD x; DWORD y; DWORD z; DWORD Resolution; DWORD type; DWORD ID; diccid_t SourceID; const void *buffer; const char *Info; const char *UserImageID; };

to use the same in c# I have done marshaling but not giving proper values when converting the pointer to structure. The C# code is follows,

        tBinary tBin = new tBinary();
        IntPtr tBinbuffer = Marshal.AllocCoTaskMem(Marshal.SizeOf(tBin));
        Marshal.StructureToPtr(tBin.bin, tBinbuffer, false);


        tDeviceProperty tDevice = new tDeviceProperty();
        tDevice.bin = tBinbuffer;
        IntPtr tDevicebuffer = Marshal.AllocCoTaskMem(Marshal.SizeOf(tDevice));
        Marshal.StructureToPtr(tDevice.bin, tDevicebuffer, false);

        Battary tbatt = new Battary();
        tbatt.value = tDevicebuffer;
        IntPtr tbattbuffer = Marshal.AllocCoTaskMem(Marshal.SizeOf(tbatt));
        Marshal.StructureToPtr(tbatt.value, tbattbuffer, false);

        result = GetDeviceProperty(ref tbattbuffer);

        Battary v = (Battary)Marshal.PtrToStructure(tbattbuffer, typeof(Battary));

        tDeviceProperty v2 = (tDeviceProperty)Marshal.PtrToStructure(tDevicebuffer, typeof(tDeviceProperty));

        tBinary v3 = (tBinary)Marshal.PtrToStructure(tBinbuffer, typeof(tBinary));