The STL includes several data structures to the developer one of them is the vector, which is a dynamic vector, there are several other structures a quick search and you will see its resources.
This is implemented with template method so that it can be reused for any type you want to use, any class declared that there is a template method must follow along with it the type you want to work, that is, what is between keys as in the example below:
pilha<int> a; // Uma pilha de inteiros
a.empilhar(1); // Empilha inteiros
pilha<pessoa> p; // Uma pilha de pessoas
p.empilhar(new pessoa("João", "155155155-15")) // Instancia uma nova pessoa e a empilha
In short, vector line_table; is a vector of pointers to line... That is, a dynamical vector that stores addresses of instances of line
vector<line *> line_table;
line l_exemplo; // Instancia de line
line_table.push_back(&l_exemplo); // inseri no final do vetor o endereço da variavel l_exemplo
Not forgetting that the & before variable indicates memory address of the variable and not content of the variable... Search by pointers if you are not aware of pointers... If you want more details about templates (how to create for example) search about templates
What context? The question is bad because one is missing. Add information to make the question understandable.
– Maniero
Alexsander, I suggest you pay attention to the comments that other users leave on their questions, they usually have valuable tips so you can make your question clear and responsive to community members.
– Math