Does ::operator new(size_t) use malloc()?

Question

Does ::operator new(size_t) call malloc() internally, or does it use system calls / OS-specific library calls directly? What does the C++ standard say?

In this answer it says that:

malloc() is guaranteed to return an address aligned for any standard type. ::operator new(n) is only guaranteed to return an address aligned for any standard type no larger than n, and if T isn't a character type then new T[n] is only required to return an address aligned for T.

And that suggests that new() cannot be required to call malloc().

Note: There's an SO question about everything operator new does other than allocation.

Answer 1

The details of how operator new is implemented are property of a particular implementation of standard library - not even a compiler or operation system. I am familiar with one (gnu) and aware of 3 others - CLang, Apache and MSFT. All of them are using malloc() within operator new, because it just makes a life of library developer so much easier.

If malloc() were not used, said developer would have to reimplement a lot in terms of memory allocation, and sprinkle the code heavily with OS-dependent logic to actually request memory. No one wants to do this when malloc() is already there. But by no means they are obliged to use it.