Thread: Overloading new for alignment

Hi. I'm trying to overload my new and delete operators so that they can be created aligned in memory. Basically what I have is:

Code:

void *operator new(size_t size) throw()
{
	return _aligned_malloc(size, 16);
}

void operator delete(void *ptr) throw()
{
	_aligned_free(ptr);
}

I was wondering if this would stil support object unwinding if I use my version of delete? Also, I am having a hard time compiling because this implementation fights with the new/delete declared in other headers. How would one avoid this type of linker error?

I'm using VC 9.0 (2008) and I'm programming a DirectX application. I did a bit of digging and one of the DirectX files overloads the new operator, so my code conflicts with it.

Error is like this:
error LNK2005: "void * __cdecl operator new(unsigned int)" (??2@YAPAXI@Z) already defined in LIBCMTD.lib

Any suggestions?

Originally Posted by Bubba

AFAIK MSVC already does alignment for you. You can specify the alignment boundary in the options.

I don't think it does, IMO. I've seen addresses that were not aligned. I know adding __declspec(align(16)) before your class/variable will guarantee that non-dynamically allocated memory is aligned to 16 bits. AFAIK, dynamically allocated classes and variables with that prefix are NOT aligned. Hence I'm trying to wrap _aligned_malloc() in a new operator.

I heard that adding a #pragma push(16) might align everything correctly, but I've yet to see it work properly.

But anyway, thats beside the point. I changed the calling convention of my project from __fastcall to __cdecl and everything works now. Thats odd that it forces me to use this convention.

Have you actually examined the alignment of your data? I believe MS alignment is at least 16 bytes on all allocations - it may even be aligned to 32 or 64 bytes at all times.

--
Mats