Question

unsigned char* Data::getAddress(unsigned char* address)
{
    strcpy((char*)address, (char*)this->_address);
    return (unsigned char*)address;
}

int main()
{
    Data d;
    d.makealinkedlisthere();
    while (d)
    {
       unsigned char address[256];
       printf("0x%08x \r\n",d.getAddress(address));
       d = d.getNext();
    }
    return 0;
}

It returns the first two (which is the same, and it should be different [can tell from the debugger]…) then crashes out.

It just makes a linked list. protected member Data* _next … a chain of them.

The unsigned char* is from Windows function VirtualQueryEx part of the MEMORY_BASIC_INFORMATION data structure it returns.

this->_address = (unsigned char*)meminfo->BaseAddress; // casted from void*

It is void*, but I see it converted to unsigned char* in other’s codes. In the debugger I can see it represented as a hex number.

D1: +    _address   0x7ffd5000 <Bad Ptr>    unsigned char * 
D1->_next:+  _address   0x7f6f0000 "áå•ú`©" unsigned char * 
D1->_next->_next+    _address   0x7ffb0000 " "  unsigned char *

Answer 1

MEMORY_BASIC_INFORMATION.Base Address is the location of the region of pages and not a string and there is no gurantee that it would be null terminated.
From the MSDN site you can see the MEMORY_BASIC_INFORMATION structure

typedef struct _MEMORY_BASIC_INFORMATION {
  PVOID  BaseAddress;
  PVOID  AllocationBase;
  DWORD  AllocationProtect;
  SIZE_T RegionSize;
  DWORD  State;
  DWORD  Protect;
  DWORD  Type;
} MEMORY_BASIC_INFORMATION, *PMEMORY_BASIC_INFORMATION;

To copy the data, you should use a memcpy with size = 255`.

Looking back to your code, provided there is no other issues, changing it to

PVOID Data::getAddress(PVOID address,size) {    
    memcpy((address, (void *)this->_address, size);
    address[size]=NULL;
    return address;
}
int main() {
    Data d;
    d.makealinkedlisthere();
    while (d) {
       unsigned char address[256];
       printf("Address: 0x%08x \n",d.getAddress((PVOID)address),sizeof(address));
       printf("Data: %s\n",(LPSTR)d.getAddress((PVOID)address),sizeof(address));
       d = d.getNext();
    }
    return 0;
}

should work

Please also note, it would be safe to store RegionSize and to do a boundary check before memcpy.