Question

I know that the standard does not force std::vector to allocate contiguous memory blocks, but all implementations obey this nevertheless.

Suppose I wish to create a vector of a multidimensional, static array. Consider 2 dimensions for simplicity, and a vector of length N. That is I wish to create a vector with N elements of, say, int[5].

Can I be certain that all N*5 integers are now contiguous in memory? So that I in principle could access all of the integers simply by knowing the address of the first element? Is this implementation dependent?

For reference the way I currently create a 2D array in a contiguous memory block is by first making a (dynamic) array of float* of length N, allocating all N*5 floats in one array and then copying the address of every 5th element into the first array of float*.

Answer 1

For reference the way I currently create a 2D array in a contiguous memory block is by first making a (dynamic) array of float* of length N, allocating all N*5 floats in one array and then copying the address of every 5th element into the first array of float*.

That’s not a 2D array, that’s an array of pointers. If you want a real 2D array, this is how it’s done:

float (*p)[5] = new float[N][5];

p [0] [0] = 42;   // access first element
p[N-1][4] = 42;   // access last element

delete[] p;

Note there is only a single allocation. May I suggest reading more about using arrays in C++?