c++stdvectoremplacestdinitializerlist

Emplacement of a vector with initializer list

i have a std::vector<std::vector<double>> and would like to add some elements at the end of it so this was my trial:

std::vector<std::vector<double> > vec;
vec.emplace_back({0,0});

but this does not compile whereas the following will do:

std::vector<double> vector({0,0});

Why can't emplace_back construct the element at this position? Or what am i doing wrong?

Solution

  • Template deduction cannot guess that your brace-enclosed initialization list should be a vector. You need to be explicit:

    vec.emplace_back(std::vector<double>{0.,0.});

    Note that this constructs a vector, and then moves it into the new element using std::vector's move copy constructor. So in this particular case it has no advantage over push_back(). @TimKuipers 's answer shows a way to get around this issue.