関連ワード:  initialize 2d vector cpp    declare 2d vector cpp    initialize 2d vector c++    initialize 2d vector c++ with 0    initialize 2d vector c++ with size    initialize 2d vector c++ with values    initialize 2d vector c++ with default value    initialize 2d vector c++ after declaration    initialize 2d vector c++ with zeros    initialize 2d vector c++ constructor