The C++ 'new' operator does seem to be supported, so I assume it has some kind of heap allocator - although I imagine that when you've only got 1 kilobyte to play with it gets quickly eaten by the allocators datastructures and C++ vtable pointers, not to mention the impact of fragmentation if you allocate any objects more than a few tens of bytes.
In any case, when all we have is 1 KB, the real answer is Assembly.
C++ really isn't my forte though.
You can also overload it, so that it can be given as implicit parameter.
Modern C++ compilers are also able to do escape analysis and remove new altogether,
https://godbolt.org/z/f9vnxG88K
If you try AVR instead of X64, the optimization will be missing, which is only a side effect of the backend not having as much attention in what it looks into.
What guarantees can you assure about the state of the application?
In any case, in this specific example for x64 it doesn't matter, because new gets optimized away.
However, if that optimization isn't done, e.g. AVR backend, then nasal daemons will be summoned.