operator new overloading and alignment

Question

I\'m overloading operator new, but I recently hit a problem with alignment. Basically, I have a class IBase which provides operator new

Answer 1

mixins are the right approach, however overloading operator new is not. This will accomplish what you need:

__declspec(align(256))  struct cachealign{};
__declspec(align(4096)) struct pagealign{};
struct DefaultAlign{};
struct CacheAlign:private cachealign{};
struct PageAlign: CacheAlign,private pagealign{};

void foo(){
 DefaultAlign d;
 CacheAlign c;
 PageAlign p;
 std::cout<<"Alignment of d "<<__alignof(d)<

Prints

Alignment of d 1
Alignment of c 256
Alignment of p 4096

For gcc, use

struct cachealign{}__attribute__ ((aligned (256)));

Note that there is automatic selection of the largest alignment, and this works for objects placed on the stack, ones that are new'd, and as members of other classes. Nor does it add any virtuals and assuming EBCO, no extra size to the class (outside of the padding needed for the alignment itself).