If you are using the vector class then you can just make a vector of vectors (array of arrays, all the same).
vector<vector<char>> gamemap
in order to build it just use
1 2 3 4
for ( i=0; i < (# of rows or row.size(), whatever size it will be); i++){
gamemap.push_back(vector<char> row)
}
return gamemap
something along those lines would build it. I don't know your specifics but this is a pretty straightforward way you can do it and if you know how to build your row vectors already then this shouldn't add to much to do what you want.
Then in order to access any give place in your gamemap it's just gamemap[i][j] and you can work with gamemap as you would any matrix really.