STL Map Question

[Yves M]

If you need it to be sorted, then yes, std::map is pretty much the only option.

Custom allocators are not *that* easy, so I can't write an example off the top of my head, but there is a good example in boost's pool library. It will definitely help with memory fragmentation if you use a custom allocator, but how you design it depends very much on your usage scenario.

But some sites say that memory space available in your machine is the limit for map.

Yes, in theory that's true, in practice you may run into other problems first.

Why do you need that many elements in the map ? Why does it have to be sorted ? Are you inserting / deleting elements during operation or is it rather a fixed structure ?

P.S. With 100.000 elements, you might still find std::map to be OK, but of course the problem is that deleting the whole data in one go is bound to be horribly slow (that's because of the allocator).