C++ vector with dynamic item size

Question

the C++ STL vector has a lot of decent properties, but only works when the size of each item is known at run-time.

I would like to have a vector class that features

Answer 1

vector represent a contiguous array in memory. This is efficient, since it can use pointer arithmetics to directly access elements by index. But doing that imply all elements having the same size, and to know this size before building the vector.

For your needs, either use a vector of pointers to elements, of a double linked list. vector of pointers is almost as fast as vector. It only needs one mode deference.

If your integers and doubles are the same size (e.g. 64 bits), you could use an union to access each item either as an integer or as a double. But you'd need a way to know what each element is supposed to be.