将void *强制转换为struct *

Question

I have this struct:

typedef struct
{
    UINT8 a;
    UINT8 len;
    BYTE *data;
} MyStruct;

and this binary array [0x00, 0x03, 0x08, 0x09, 0x0a] which is assigned to a void* variable "BINDATA".

How can I cast BINDATA to MyStruct and be able to access its "data" field?

I tried:

MyStruct *myStruct = (MyStruct*) BINDATA;

After that I was able to access:

myStruct->a; //gave me 0x00
myStruct->len; //gave me 0x03

But I could not access

myStruct->data;

without memory access violation. I guess this is because "data" address pointer gets set to 0x08 and not its value.

Answer 1

Instead of BYTE *data you should use BYTE data[0] or (if your compiler doesn't like this) BYTE data[1] . The difference between pointer and array here is crucial - array is "data that is right here" while pointer is "data somewhere else" which is not your case.

Answer 2

Something like this may work in c++:

UINT* a1 = &myStruct->len;
UINT* a2 = ++a1;

Then cast a2 to whatever you want. Be aware of the size and the type of your data.