Initializing both dimensions of a vector of vectors inside a class

Question

I have a class

class A
{
    private:   
        std::vector< std::vector<int> > v;
    //other statements
}

I would like to initialize both dimensions of this vector by passing them to the constructor of the class, possibly using initializer lists.

This question asks about the same question for a vector of integers, and this asks about initialization of a vector of vectors, but outside any class. I want to initialize the sizes of both dimensions, but the vector is a class member.

How can I do this?

use the second method, put them at [member initializer lists](http://en.cppreference.com/w/cpp/language/initializer_list) (or you can use resize inside constructor body) — apple apple, Jan 13 '17 at 16:42
@appleapple Thank you, but how do I use it to initialize both dimensions? — GoodDeeds, Jan 13 '17 at 16:43

apple apple · Accepted Answer · 2017-01-13T16:56:47.180

5

you can put them in the member initializer lists

like this

class A{
public:
   A(int dim1,int dim2):v(dim1,std::vector<int>(dim2)){}
private:   
   std::vector< std::vector<int> > v;
};

or you can use vector::resize

class A{
public:
   A(int dim1,int dim2){v.resize(dim1,std::vector<int>(dim2));}
private:   
   std::vector< std::vector<int> > v;
};

edited Jan 13 '17 at 16:56

answered Jan 13 '17 at 16:46

apple apple

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score 2 · Answer 2 · answered Jan 13 '17 at 17:52

Did you want to initialise with existing data?

struct Matrix
{
    Matrix(std::initializer_list< std::initializer_list<int> > ilil)
    {
        data_.reserve(ilil.size());
        for (auto&& il : ilil)
        {
            data_.emplace_back(il);
        }
    }

    std::vector< std::vector<int> > data_;
};

void test()
{
    auto m = Matrix {
        { 1, 2, 3 },
        { 4, 5, 6 },
        { 7, 8, 9 }
    };
}

Initializing both dimensions of a vector of vectors inside a class

2 Answers2