用于2D矢量的C ++插入命令不起作用

Question

My program is very long so I would just simplify the problematic codes here:

class C{...};

vector<vector<C>> A;
vector<C> B;

int i = 0;
cin >> i;

A.insert(A.begin()+i, B); 

Here, when I change the last line to "A.push_back(B);" or "A.insert(A.begin()+0, B), the run-time error is gone, therefore I suspect the problem is with the 2d vector size and position. But I just want the vector B to be inserted into the 2d vector A at a specific position only! Please help :'(

Answer 1

Your vector has zero size.

While vectors are 'dynamic' structures, they don't grow of their own accord. Accessing elements outside the current bounds will result in undefined behaviour.

If you want the vector to have at least i elements, you can do this before the insert.

if (i < A.size())
  A.resize(i)