How do I iterate over a 2D vector in C++11?

How do I iterate over a 2D vector in C++11?

You can use nested loops to iterate over a 2D vector in C++11. Here's an example:

#include <vector>
#include <iostream>

int main() {
    std::vector<std::vector<int>> vec = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
    for (const auto& row : vec) {
        for (const auto& elem : row) {
            std::cout << elem << ' ';
        }
        std::cout << '\n';
    }
    return 0;
}

What if I want to access elements using indices?

You can access elements using indices like this:

int value = vec[i][j]; // where i is the row index and j is the column index

Can I use range-based for loops for this?

Yes, range-based for loops are a great way to iterate over a 2D vector. Here's how you can do it:

for (const auto& row : vec) {
    for (const auto& elem : row) {
        // process elem
    }
}

What if my 2D vector is empty?

If your 2D vector is empty, the loops will simply not execute. You can check if it's empty using vec.empty() before iterating.