Multi-Dimensional Vector Initialization in C++ – How to Guide

c++initializationstlvector

I have following std::vector declaration:

std::vector<std::vector<std::vector<int> > > m_input;

I am initializing it as follows:

    m_input.resize (100);
    m_output.resize(100);
    for (int i = 0; i < 100; ++i) {
        m_input [i].resize(100);
        m_output[i].resize(100);
        for (int j = 0; j < 100; ++j){
            m_input [i][j].resize(100);
            m_output[i][j].resize(100);
        }
    }

How can I achieve this via the member initializer list?

Best Answer

std::vector<T> has a constructor that takes two arguments, a number of elements and an initial value. In your case, you want to initialize m_input with 100 copies of a std::vector<std::vector<int> > , so it'd be : m_input(100, X). Now, that X in turn is a vector of 100 std::vector<int>, which in turn contains a hundred ints:

: m_input(100, std::vector<std::vector<int> >(100, std::vector<int>(100, 0)))

Related Solutions

C++ – Initialization of a Vector of Vectors

For the single vector you can use following:

typedef int type;
type elements[] = {0,1,2,3,4,5,6,7,8,9};
vector<int> vec(elements, elements + sizeof(elements) / sizeof(type) );

Based on that you could use following:

type matrix[2][2]=
{
   {1,0},{0,1}
};

vector<int> row_0_vec(matrix[0], matrix[0] + sizeof(matrix[0]) / sizeof(type) );

vector<int> row_1_vec(matrix[1], matrix[1] + sizeof(matrix[1]) / sizeof(type) );

vector<vector<type> > vectorMatrix;
vectorMatrix.push_back(row_0_vec);
vectorMatrix.push_back(row_1_vec);

In c++0x, you be able to initialize standard containers in a same way as arrays.

C++ – How to Initialize Vector of Vectors

std::vector<std::vector<T>> my_vec(m, std::vector<T>(n))

Be careful that Ts default constructor is called for each of m * n members of the matrix.

Best Answer

Related Solutions

C++ – Initialization of a Vector of Vectors

C++ – How to Initialize Vector of Vectors

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