How might I overload the "new" operator to allocate memory from a secondary memory device?

Question

I am looking for a syntax to allocate memory from a secondary memory device and not from the default heap.

How can i implement it? Using malloc() would by default take it from heap... Surely there must be another way!

Answer 1

You'd have to build or adapt your own heap manager, and overload new and delete, as well as new[] and delete[]. Initialize the heap manager with the special memory.

Answer 2

#include <new>

void* operator new(std::size_t size) throw(std::bad_alloc) {
  while (true) {
    void* result = allocate_from_some_other_source(size);
    if (result) return result;

    std::new_handler nh = std::set_new_handler(0);
    std::set_new_handler(nh);  // put it back
    // this is clumsy, I know, but there's no portable way to query the current
    // new handler without replacing it
    // you don't have to use new handlers if you don't want to

    if (!nh) throw std::bad_alloc();
    nh();
  }
}
void operator delete(void* ptr) throw() {
  if (ptr) {  // if your deallocation function must not receive null pointers
    // then you must check first
    // checking first regardless always works correctly, if you're unsure
    deallocate_from_some_other_source(ptr);
  }
}
void* operator new[](std::size_t size) throw(std::bad_alloc) {
  return operator new(size);  // defer to non-array version
}
void operator delete[](void* ptr) throw() {
  operator delete(ptr);  // defer to non-array version
}