Struggling with pointers to Assign new contents to a vector - c++

Question

Okay so what I am trying to do is add an instance of a class to a specific index of a vector. This index can either be initially non-existent, or be an existing index which has been cleared and is having a new class instance being written to that position.
Below is the function that I have been using to try and write these instances to the vector, and commented at the bottom you can see the other 2 methods that I tried to use, Obviously with push_back only being able to add new vectors at the end.
I have a feeling that assign may only be able to add data to existing elements? And that insert may add a new element and shift the existing elements down instead of overwriting. Just want a bit of clarity on this, as the C++ tutorials have started confusing me.
Also, what would be the correct way to reference/defreference/call the Person vector (in this case being referred to as "allthePeople"), so that it is possible to change its data?
void createnewPerson(int assignID, RECT startingpoint, vector<Person>* allthePeople, int framenumber) {
Person newguy(assignID, startingpoint, framenumber);
std::cout << "New Person ID number: " << newguy.getIDnumber() << std::endl;
std::cout << "New Person Recent Frame: " << newguy.getlastframeseen() << std::endl;
std::cout << "New Person Recent history bottom: " << newguy.getrecenthistory().bottom << std::endl;
int place = assignID - 1;
//This is where I am confused about referencing/dereferencing
allthePeople->assign(allthePeople->begin() + place, newguy);
//allthePeople->insert(place, newguy);
//allthePeople->push_back(newguy);
}
Also just to clarify, "place" is always 1 less than "assignID", because vector positions start at 0, and I simply wanted to start their ID numbers at 1 instead of 0.
-------------EDIT : ADDED IF LOOP THAT SOLVED PROBLEM-----------------
void createnewPerson(int assignID, RECT startingpoint, vector<Person>* allthePeople, int framenumber) {
Person newguy(assignID, startingpoint, framenumber);
std::cout << "New Person ID number: " << newguy.getIDnumber() << std::endl;
std::cout << "New Person Recent Frame: " << newguy.getlastframeseen() << std::endl;
std::cout << "New Person Recent history bottom: " << newguy.getrecenthistory().bottom << std::endl;
int place = assignID - 1;
if (allthePeople->size() > place)
{
//assuming places starts from 1 to vector's size.
(*allthePeople)[place] = newguy;
}
else
{
allthePeople->push_back(newguy);
}
}

Answer 1

assign is meant to replace the full content of a vector.
Assuming that you want to put every person in a specific place. You might then better use operator[] to put the value at the place you want instead of using assign. You need to have the vector with the appropriate size.
if (allthePeople->size() >= place )
{
//assuming places starts from 1 to vector's size.
(*allthePeople)[place - 1] = newguy;
}