関連ワード:  how to create an empty vector in cpp    how to initialize an empty vector in cpp    how to declare an empty vector in cpp    how to create an empty vector in c++    how to initialize an empty vector in c++    how to initialize an empty 2d vector in c++    how to declare an empty 2d vector in c++    how to make empty vector c++    is empty vector c++    size of empty vector c++