allocating vectors (or vectors of vectors) dynamically
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));
You're conflating two issues, dynamic allocation and resizable containers. You don't need to worry about dynamic allocation, since your container does that for you already, so just say it like this:
matrix name(sizeX, std::vector<double>(sizeY));
This will make name
an object with automatic storage duration, and you can access its members via name[i][j]
.