从向量C ++中删除多个元素

Question

Here is some code which checks if 2 units are killed after they attack each other, I pass in the position in the vector however when I remove one the vector is changed in size and therefore the 2nd unit is out of range. How can I remove both simultaneously?

if ((MyHealth <= 0) && (EnemyHealth <= 0))
{
    PlayerUnits.erase(PlayerUnits.begin() + MyUnit, PlayerUnits.begin() + EnemyUnit);
}
else if (MyHealth <= 0)
{
    PlayerUnits.erase(PlayerUnits.begin() + MyUnit);
}
else if (EnemyHealth <= 0)
{
    PlayerUnits.erase(PlayerUnits.begin() + EnemyUnit);
}

Answer 1

Instead of coding the removal logic yourself, it would be better managed using std::remove_if from algorithm . Depending on whether you have compiler supporting C++11 or not, the Predicate can either be a lambda or a named function.

Answer 2

First point: In your first block, the call erase(x, y) does something different than you expect - it erases a whole range of elements starting at index x until just before index y. For example, if we have the vector [a,b,c,d,e,f,g], then erase(2,5) will erase indexes 2,3,4, so we end up with [a,b,f,g]. I'm guessing you want to erase just two elements, not an entire range.

Second point: As Dieter Lücking pointed out, simply erase the higher index element first, like this:

if (MyUnit > EnemyUnit) {
    PlayerUnits.erase(PlayerUnits.begin() + MyUnit);
    PlayerUnits.erase(PlayerUnits.begin() + EnemyUnit);
} else {
    PlayerUnits.erase(PlayerUnits.begin() + EnemyUnit);
    PlayerUnits.erase(PlayerUnits.begin() + MyUnit);
}

Answer 3

I think a better way to handle this would be to add an "isDead" condition to your "unit" class:

void Unit::Update()
{
    //other stuff
    if(this->m_health <= 0) this->m_isDead = true;
}

then in the main loop:

void Game::Update()
{
   size_t size = PlayerUnits.size();

   //iterate backwards, so there is no skipping
   for(int i = size-1; i>= 0; i--)
   {
       PlayerUnits[i]->Update();
       if(PlayerUnits[i]->isDead()) PlayerUnits.erase(PlayerUnits.begin() + i);
   }
}

This is at least how I personally do it.