Manipulation iterator list + pointers - c++

Question

I'm trying to check all collisions of all entities. I do it like:
My parent Class "Entity" has a static std::list<Entity*> allEntities
The constructors of all child class have this sentence Entity::AddEntity((*this));
I have a property std::list< Entity*> m_collisionWith; it will take all pointers of entities with intersection
After, I have a static function in the Entity class :
for (std::list<Entity*>::iterator it = allEntities.begin(); it != allEntities.end(); it++) //to check everything...
{
for (std::list<Entity*>::iterator itSec = allEntities.begin(); itSec != allEntities.end(); itSec++) // ... with everything
{
if ((*it)->m_spriteCharacter[(*it)->m_currentFrameCharacter].getGlobalBounds().intersects((*itSec)->m_spriteCharacter[(*itSec)->m_currentFrameCharacter].getGlobalBounds()) && *itSec != (*it)) //to_check if we have an intersection between two objects
{
if ((*it)->m_collisionWith.empty())
{
(*it)->m_collisionWith.push_back((*itSec));
}
else
{
for (std::list<Entity*>::iterator itThr = (*it)->m_collisionWith.begin(); itThr != (*it)->m_collisionWith.end(); itThr++)
{
if ((*itThr) != (*itSec)) //to check if the second object is not here yet. itThr will be every objects in m_collisionWith
{
(*it)->m_collisionWith.push_back((*itSec));
}
}
}
}
}
}
So I would like to check if an entity has an intersection with an another entity and if it is, I would like not add it in the m_collision.
Normally, if I have 3 entities, m_collision.size() is equals 3 but it is growing up nonstop

Answer 1

for (std::list<Entity*>::iterator itThr = (*it)->m_collisionWith.begin(); itThr != (*it)->m_collisionWith.end(); itThr++)
{
if ((*itThr) != (*itSec)) //to check if the second object is not here yet. itThr will be every objects in m_collisionWith
{
(*it)->m_collisionWith.push_back((*itSec));
}
}
This pushes itSec at the back for every element in (*it)->m_collisionWith that is not equal to *itSec. It should be:
bool exists = false;
for (std::list<Entity*>::iterator itThr = (*it)->m_collisionWith.begin(); itThr != (*it)->m_collisionWith.end(); itThr++)
{
if ((*itThr) != (*itSec)) //to check if the second object is not here yet. itThr will be every objects in m_collisionWith
{
exists = true;
break;
}
}
if (!exists)
{
(*it)->m_collisionWith.push_back((*itSec));
}