C++ - Map contains way too many elements - c++

Question

I'm attempting to create a entity manager for a game I'm making so I can easily manage all the entities within the game (Player, Enemies, Objects) and be able to call their Update and Render functions without having to do it manually.
I'm recording the entities using a map that takes in a int and a Entity class
std::map<int, Entity*> entities;
Whenever the Entities are added to the map, they'll also be given a random ID with that ID being added to a vector just so I can record what ID's have been used so I don't end up using the exact same entity
IDS = std::vector<int>();
void EntityManager::AddEntity(Entity* entity)
{
int ID = rand();
for(int i = 0; i < IDS.size(); i++)
{
if(IDS[i] == ID)
{
ID = rand();
i = 0;
}
}
entities.insert(pair<int, Entity*>(ID, entity));
}
I then finally call the Update and Render functions of each entity
void EntityManager::Update(float deltaTime)
{
if(!entities.empty())
{
for(int i = 0; i < entities.size(); i++)
{
if(entities[i] != nullptr)
{
entities[i]->Update(deltaTime);
}
}
}
}
void EntityManager::Render()
{
if(!entities.empty())
{
for(int i = 0; i < entities.size(); i++)
{
if(entities[i] != nullptr)
{
entities[i]->Render();
}
}
}
}
The problem I'm having is the frame rate will instantly drop to something like 2FPS as it seems when I'm checking the size of the map within the Update and Render functions, the size is something like 16587 instead of what it should be which is just 2 as at this point I'm only inputting 2 entities into the map.
I've tried to figure out what the cause is but I just can't find it, the size is 2 after the "entities.insert" in the AddEntity function but once the Update and Render functions are called, the size instantly goes to 16587 or some number like that. I'm not calling AddEntity anywhere else except for in a constructor within another class:
entityManager->AddEntity(player);
entityManager->AddEntity(diamond);

Answer 1

entities is a map, and you're using random integers as the key. You cannot use an index loop to access the members of the map. Every iteration of that loop will add another entry in the map (with a nullptr Entity), increasing the size causing your loop to continue on.
To iterate thru the map, you can use
for (const auto &ent: entities)
ent.second->Render();
then you'd only see the entries in the map and not add any new ones.