Question

I want to create a vector<vector<int>> where the outer vector is fixed (always containing the same vectors), but the inner vectors can be changed. For example:

int n = 2; //decided at runtime
assert(n>0);
vector<vector<int>> outer(n); //outer vector contains n empty vectors

outer.push_back(vector<int>()); //modifying outer vector - this should be error

auto outer_it = outer.begin();
(*outer_it).push_back(3); //modifying inner vector. should work (which it does).

I tried doing simply const vector<vector<int>>, but that makes even the inner vectors const.

Is my only option to create my own custom FixedVectors class, or are there better ways out there to do this?

Answer 1

Wrap the outer vector into a class which just provides at, begin, end and operator []. Let the class take only have one constructor taking its capacity.

This most probably the best way.