vector of vectors push_back

Question

I'm designing a multilevel queue process simulator in C++ but I've got a problem when trying to implement several queues (my queues are vectors).So, "multilevel" is a 4 elements array (not vector). Inside each of those elements there is a vector (type t_PCB). ``` vector> multilevel[4]; ``` My question is: How can i insert an element at the end of one these 4 `t_PCB` vectors? Thank you in advance. I've tried the code line below but it doesn't work (error: not matching member function for call 'push_back') ``` multilevel[0].push_back(p); //where "p" is a t_PCB object ``` The line from above can not be used when talking about "multilevel" because this array only accepts arguments type: vector < t_PCB > So, as I ask at the beginning: how can I push an object type "t_PCB" inside "multilevel"?

Accepted Answer

By doing this: ``` vector > multilevel[4]; ``` You declare an array of four zero-sized `vectors`, each of which can contain objects of type `vector`. What you probably wanted to do is rather: ``` vector > multilevel(4); // ^^^ ``` This will instantiate a vector of four default-initialized objects of type `vector`. Then, you can just do: ``` multilevel[size].push_back(p); ``` Notice, though, that vector indices (like array indices) are zero-based, so `size` must be less than the size of the vector. In the above expression, the sub-expression `multilevel[size]` returns a reference to the `size`-th vector inside `multilevel`, and on that vector you are then invoking the member function `push_back(p)`, which appends element `p` to it.

vector of vectors push_back

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