How is dynamic memory managed in std::vector?

Question

How does std::vector implement the management of the changing number of elements: Does it use realloc() function, or does it use a linked list?

Thanks.

Answer 1

One of the hard-and-fast rules of vectors is that the data will be stored in one contiguous block of memory.

That way you know you can theoretically do this:

const Widget* pWidgetArrayBegin = &(vecWidget[0]);

You can then pass pWidgetArrayBegin into functions that want an array as a parameter.

The only exception to this is the std::vector specialisation. It actually isn't bools at all, but that's another story.

So the std::vector will reallocate the memory, and will not use a linked list.

This means you can shoot yourself in the foot by doing this:

Widget* pInteresting = &(vecWidget.back());
vecWidget.push_back(anotherWidget);

For all you know, the push_back call could have caused the vector to shift its contents to an entirely new block of memory, invalidating pInteresting.