To expand on what AP said. Vectors, and most dynamic containers or classes essentially hold pointers, maybe a cached size variable. But if you have a vector such as your example above
vector<Player> players;
and you do a
size_t so = sizeof(players);
You will get the same result for an empty players vector as you would with a players vector with 10000 players in it. The sizeof a class is fixed at compile time, and if you make a vector on the stack, thats the about of stack space that will be used.
As you push stuff onto it, or pop stuff off, the vector itself manipulates memory from the heap, and this memory is dependant on what you are storing, and how many you are storing.
When you do
vector<Player> players(i);
You are telling the constructor of the vector to initialize with a size of i, so it will allocate from the heap something like new Player
; The capacity and size of the vector will probably both be set to i by the time its done.
The first method creates an empty vector. I think its implementation defined as to the initial capacity of the vector, but as you push things on, the vector has to grow when it runs out of room, usually by 1.5 or 2x the size each time it grows(again implementation specific). Depending on how many players your loop pushes onto the vector, the vector will end up with the size() of that many players, but the capacity() of the vector could be much more, resulting in wasted memory. Again not a big deal for a text rpg, but important to understand. This is why most people will recommend that if you know up front how many items you will be added to a vector to go ahead and reserve() the space in the vector for it, so that the vector doesn't have to do any costly resizing during runtime.
Edit: an additional detail. Remember, the vector<Player> players(i); method of initialization sets the size of the vector to i, so when you go filling in the values you need to do so with players[] = ?, and not push_back(). With push_back you are adding to the end of the array. In this example the vector would be initialized with i player objects default constructor.
Since it appears you meant for it to be a vector<Player*> players(i); you might want to use the 2 parameter constructor to initialize the value of the elements to null, such as vector<Player*> players(i, NULL); to ensure that all the pointers are not some garbage values.
Although MSDN says that not including the 2nd parameter will default it to 0, at least for their vector<int> example, I'm not entirely sure if this is their implementation or part of the standard.
