std::vector and contiguous memory of multidimensional arrays
c++, contiguous, memory-management, standards, vector
Solution
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++?
Problem
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*`.