C++ – Initializing a Two-Dimensional std::vector

c++initializationstdvectorvector

So, I have the following:

std::vector< std::vector <int> > fog;

and I am initializing it very naively like:

for(int i=0; i<A_NUMBER; i++)
{
    std::vector <int> fogRow;
    for(int j=0; j<OTHER_NUMBER; j++)
    {
         fogRow.push_back(0);
    }
    fog.push_back(fogRow);
}

And it feels very wrong… Is there another way of initializing a vector like this?

Best Answer

Use the std::vector::vector(count, value) constructor that accepts an initial size and a default value:

std::vector<std::vector<int> > fog(
    ROW_COUNT,
    std::vector<int>(COLUMN_COUNT)); // Defaults to zero initial value

If a value other than zero, say 4 for example, was required to be the default then:

std::vector<std::vector<int> > fog(
    ROW_COUNT,
    std::vector<int>(COLUMN_COUNT, 4));

I should also mention uniform initialization was introduced in C++11, which permits the initialization of vector, and other containers, using {}:

std::vector<std::vector<int> > fog { { 1, 1, 1 },
                                    { 2, 2, 2 } };
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