使用开始和结束迭代器时出错

Question

vector <vector<int> > v8;
int N;
cin >> N;
for (int i = 0; i < N; i++)
{
    int n;
    cin >> n;
    vector <int> temp;
    for (int i = 0; i < n; i++)
    {
        int x;
        cin >> x;
        temp.push_back(x);
    }
    v8.push_back(temp);
    
}

vector <int> ::iterator it;
for (it = v8.begin(); it < v8.end(); it++)
{
    cout << (*it) << " ";
}

我收到这个错误：

no operator "=" matches these operandsC/C++(349)
intro.cpp(161, 13): operand types are: __gnu_cxx::__normal_iterator<int *, std::vector<int, std::allocator<int>>> = __gnu_cxx::__normal_iterator<std::vector<int, std::allocator<int>> *, std::vector<std::vector<int, std::allocator<int>>, std::allocator<std::vector<int, std::allocator<int>>>>>

我该如何解决？？

Answer 1

问题是it是一个迭代器到一维vector<int>而b8.begin()给我们一个 2D vector<vector<int>> 的迭代器。所以这些迭代器彼此不兼容。也就是说，你不能使用迭代器it来遍历一个二维向量。

您可以通过更改 vector <int> ::iterator it; 来解决此问题，如下所示：

    vector <vector<int>> ::iterator it;   //change made here. Now it is an iterator to a 2D vector
    for (it = v8.begin(); it != v8.end(); it++)  
    {
        
        for(auto i = (*it).begin(); i != (*it).end();++i) // i is an iterator to a 1D vector
        {
            cout << (*i) << " ";//it changed to i
        }
        
    }

另一种选择是使用 auto 和 range-based for 循环，如下所示：

for (auto &row: v8)
{
    for(auto &col: row)
    {
        cout << col << " ";
    }
      
}

Answer 2

要遍历 v8 中的向量，枚举它们的元素，请使用 range-based for 循环。

for (auto& v: v8) {
    for (auto& it: v) {
        std::cout << it << ' ';
    }
}

使用开始和结束迭代器时出错

Getting an error while using begin and end iterators

c++

stl

c++11