在C++中如何正确地初始化和遍历一个二维数组

int arr[3][3] = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

int arr[3][3] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
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<p>未显式赋值的元素会自动初始化为0：</p><p><span>立即学习</span>“<a href="https://pan.quark.cn/s/6e7abc4abb9f" style="text-decoration: underline !important; color: blue; font-weight: bolder;" rel="nofollow" target="_blank">C++免费学习笔记（深入）</a>”；</p>
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int arr[2][2] = {{1}}; // 结果是 {{1, 0}, {0, 0}}

#include <vector>
std::vector<std::vector<int>> vec(3, std::vector<int>(3, 0)); // 3x3 全0

for (int i = 0; i < 3; ++i) {
    for (int j = 0; j < 3; ++j) {
        std::cout << arr[i][j] << " ";
    }
    std::cout << std::endl;
}

for (const auto& row : arr) {
    for (const auto& elem : row) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;
}

for (const auto& row : vec) {
    for (int val : row) {
        std::cout << val << " ";
    }
    std::cout << "\n";
}

for (size_t i = 0; i < vec.size(); ++i) {
    for (size_t j = 0; j < vec[i].size(); ++j) {
        // 安全访问 vec[i][j]
    }
}