Usage of insert() in vector

vector in insert() Functions have the following three uses : 
1、 At a designated location loc The value inserted before is val The elements of , Returns the iterator that points to this element
2、 At a designated location loc Insert before num The values are val The elements of  

3、 At a designated location loc Insert interval before [start, end) All elements of

Specify address insertion value ：

v.insert(lower_bound(v.begin(), v.end(), st[top]), st[top]);