C++ copying multidimensional vector

c++, copy, multidimensional-array, vector

Solution

There are a few problems with your code. By the end of line 4, you have two vectors that each contain 10 empty vectors. You could visualize it like this:

a = {{}, {}, {}, {}, {}, {}, {}, {}, {}, {}}
b = {{}, {}, {}, {}, {}, {}, {}, {}, {}, {}}

Those inner vectors still do not have any elements so when you try and set `a[0][0]` to `123`, you're accessing an element that doesn't exist, invoking undefined behaviour.

If that had worked, your use of `std::copy` would simply copy each of the vectors from `a` and pushed it to the back of `b`. Since `b` already has 10 elements, it would now have 20 elements.

Then you try to output `b[0][0]` which doesn't exist just as much as `a[0][0]` didn't either.

The solution here is to simply use the copy assignment operator defined by `std::vector`:

vector<vector<int>> a = {{1, 2, 3}, {4, 5}};
vector<vector<int>> b;
b = a;

Problem

I'm having problems copying a multidimensional vector, I've tried many things but this is the last one: ``` vector < vector < int > > a; vector < vector < int > > b; a.resize(10); b.resize(10); a[0][0] = 123; copy( a.begin(), a.end(), back_inserter(b) ); cout << b[0][0]; ``` I'm trying to do a recursive loop that counts all possible routes in a grid within 10 moves. I'm trying to create a vector called `current_path` which would hold the current path for each recursion, when the `current_path` has 10 moves, It will copy the data from `current_path` to `all_paths`. The grid goes like this: ``` 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ``` You can only move to a square you touch so from 0 you can move to 1, 4 and 5. And from 1 to 3, 4, 5, 6 etc. The main idea is to copy the `current_path` to the next function call (recursive) so it would hold the `curren_path` up to that point, doing that until it's full (10 steps). After it's copied from `current_path` to `all_paths` I suppose I have to delete the `current_path`? I know how to efficiently calculate all steps but I'm having trouble copying the `current_path` and propably and how do I add the `current_path` to `all_paths` when I'm at 10 steps?

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