c++ - allocating vectors (or vectors of vectors) dynamically

Question

I need to dynamically allocate 1-D and 2-D arrays whose sizes are given at run-time.

I managed to "discover" std::vector and I think it fits my purposes, but I would like to ask whether what I've written is correct and/or can be improved.

This is what I'm doing:

#include <vector>

typedef std::vector< std::vector<double> > matrix;

//... various code and other stuff

std::vector<double> *name = new std::vector<double> (size);
matrix *name2 = new matrix(sizeX, std::vector<double>(sizeY));

Answer 1

Dynamically allocating arrays is required when your dimensions are given at runtime, as you've discovered.

However, std::vector is already a wrapper around this process, so dynamically allocating vectors is like a double positive. It's redundant.

Just write (C++98):

#include <vector>

typedef std::vector< std::vector<double> > matrix;
matrix name(sizeX, std::vector<double>(sizeY));

or (C++11 and later):

#include <vector>

using matrix = std::vector<std::vector<double>>;
matrix name(sizeX, std::vector<double>(sizeY));