在2D std :: vector C上每个c ++ 11都不起作用？

Question

Initialize a 2D vector called matrix.

std::vector<std::vector<int>> matrix(512,std::vector<int>(512));

Now I want to resize it:

This works:

    matrix.resize(50);
    for(int i = 0; i<matrix.size() ; i++)
        matrix[i].resize(50);

And this does not work:

    matrix.resize(50);
    for(auto ele : matrix)
        ele.resize(50);

I am using for(auto ele : container) in other places, I should have support for C++11, using Microsoft Visual C++ Compiler 12.0.

Answer 1

You are making copies of the inner vectors in each loop iteration. You need to use a reference:

for(auto& ele : matrix)
        ele.resize(50);