Question

Lets say I have a std::vector of const std::strings.

std::vector<const std::string> strs;

Now the default behavior here is that the actual string containers can be allocated anywhere on the heap, which pretty much disables any prefetching of data when iterating over the contained strings.

strs.push_back("Foo"); // allocates char block on heap
strs.push_back("Boo"); // allocates char block on heap

However, since the strings are “const” I would like the char blocks to be allocated contiguously or close to each other (when possible) in order to have the most efficient cache behavior when iterating over the strings.

Is there any way to achieve this behavior?

Answer 1

You need a custom allocator known as a memory region allocator. You can look on Wikipedia or Google for more information, but the basic idea is something akin to the hardware stack- allocate one large chunk and then simply increment the pointer to mark it as used. It can serve many contiguous requests very quickly but can’t deal with frees and allocations- all freeing is done at once.