c++ - "snake" run error

Question

i'm making a simple snake game in c++. it compiles, but won't run. i'm using netbeans on a mac, and i've never had a problem like this before, so i assume it's a problem with my code:

#include <vector>
std::vector<std::vector<int> > snake;//the snake
int main(){
    snake[0][0]=0;
}

i think it might be a problem with the 2d vector.

Answer 1

snake[0][0] = 0具有未定义的行为，因为您试图分配给不存在的向量元素。

也就是说 -snake.size() == 0因此访问第一个元素snake[0]不是有效的操作。