Mastering the C++17 STL

Inserting and erasing in a std::vector

vec.push_back(t) adds an item to the end of the vector. There is no corresponding .push_front() member function, because as you can see from the diagram at the start of this section, there's no efficient way to push anything onto the front of a vector.

vec.emplace_back(args...) is a perfect-forwarding variadic function template that acts just like .push_back(t), except that, instead of placing a copy of t at the end of the vector, it places a T object constructed as if by T(args...).

Both push_back and emplace_back have what is called "amortized constant time" performance. To see what this means, consider what would happen to a naive vector if you call v.emplace_back() a hundred times in a row. With ...