Hey Guys,
I am trying to do in place initialization of an array of variables.
Essentially allocate memory. Pass in the void * into operator new[] to initialize an array of variables.
Now I get an address 4 bytes ahead of the allocated address !!
Example:
void *pMem = malloc(sizeof(A) * 4);
A *pArr = new (pMem) A[4];
pArr is (char *)pMem + 4 !!
Can anyone shed light on why ?
I noticed the first 4 bytes of pMem contains the number of elements in array. (in this case 4).
I could potentially move the pointer back and forth. But I want to know is this 4 Bytes same for any platform ? Is it same for 32 bit and 64 bit applications ??
Is this part of the C++ standard ?
Thanks !!
Jerry
/*********** Source Code *********/
class BaseString
{
enum EAllocationSource {AS_DATA, AS_HEAP};
EAllocationSource m_allocationSource;
union
{
const char *m_strStatic;
char *m_strDynamic;
};
unsigned int *m_pNumRef;
unsigned int m_len;
static const char m_nullString;
public:
virtual ~BaseString(){}
static void *operator new[] (size_t size, void *ptr)
{
printf("\nSize obtained in operator new[] function of class: %u", (unsigned int)size);
return ptr;
}
static void operator delete[] (void *val, void *ptr)
{
printf("\nAddress passed to delete in Class: %u", (unsigned int)val);
printf("\nIn Place Address passed in Class: %u", (unsigned int)ptr);
}
};
void main()
{
printf("\nSize to be allocated: %u", sizeof(BaseString) * 4);
void *pMem = malloc(sizeof(BaseString) * 4);
printf("\nAllocated Address: %u", (unsigned int)pMem);
BaseString *pArr = new (pMem) BaseString[4];
printf("\nReturned Address: %u", (unsigned int)pArr);
pArr->operator delete[](pArr, pMem);
printf("\nuint first: %u", *((unsigned int *)pMem));
while(true)
SwitchToThread();
}
