cout部分会段错误
```c++
vector<int>::iterator it = vec.begin();
vec.insert(vec.begin(),888);
for(; it != vec.end(); it++)
cout<< *it << endl;
```c++
vector<int>::iterator it = vec.begin();
vec.insert(vec.begin(),888);
for(; it != vec.end(); it++)
cout<< *it << endl;