It is difficult to implement multiple allocation strategies in the same application. In another time, I actually did quite a bit of work in this area: http://accu.org/index.php/articles/1308
Are you trying to argue that C++ programs can't use custom allocators because of language restrictions? That's demonstrably false; Gecko and WebKit, just to name a couple of C++ codebases I'm relatively familiar with, use custom allocators everywhere.
Do you mean something like operator overloading where a given type has a different implementation of new that is used for it? Or a way to select different implementations of the global operator new at runtime? It seems to me that it should be possible for the latter to make it switchable, although the code would be inelegant to say the least.
AFAIK the former is possible as well, but the problem is that I think the type-specific operator new/delete have to be members of the type which means that you can't add it on later.
That's a great article btw.
That would be a gigantic change to the language, which I'm sure I don't understand the implications of.
After thinking about this some more, I'm going to stand by my original, even if poorly argued, comment that C++ doesn't really live up to the promise of "precise control" when it comes to memory allocation, and this is one area that can have a big effect on performance. C++ has all the overhead of a low level language, with a promise of control that when you really need it is often difficult to access.
The problem with C++ is exactly the opposite, it has too many options, which makes it difficult to create a global memory management policy, unless you define you own complete framework. Quite the opposite of what you said.
I won't opine on whether it actually is unnecessary.
Now you're correct that the standard library provided with C++ does not quite give you this same level of control. If you want node elements placed somewhere specific you either have to pick the right container, write a custom allocator (including rebind support so that any required container-internal elements also can use your allocator), etc.
But this is a complaint about a C++-only feature that C doesn't even provide.
On the very few times that C does provide an standard library function that will automatically allocate storage from the heap, it is even less customizable than the C++ equivalent. Normally your only option is something allocated with malloc(3), you're told to use free(3) when appropriate, and if you need something different you run into trying to replace malloc/free and friends and then somehow telling your custom malloc when to use custom behavior and when to use stdlib behavior. But you could do this in C++ code too.
Now you can certainly easily write your own library with better support for custom allocation/deallocation. Things like the Apache Portable Runtime, for instance, or glib.
But once you've bought into the idea of simply ignoring the language standard library anyways, you've bought into something else that you could do in C++ if you really felt like it were useful.
The problem with C++ is that the standard library makes it almost straightforward to do what you want and still be able to use standard containers without having to write your own, but we have to remember that we're talking about a problem that essentially can't even be spoken about in C. So it's not so much that C "doesn't have a problem", as that this problem couldn't even be expressed in C.