The swap function is a data exchange of two containers;
Realization of ideas: Create a container data (str_sq) and empty container vector of anonymous exchange of data, the data container emptying data.
Anonymous empty container will automatically be destroyed
Remember do not be emptied with a clear function in .empty () is 0 although the time, but the memory of the data is still there.
vector<string>().swap(str_sq);//清空容量