About STL vector.erase

This is a discussion on About STL vector.erase within the C++ Programming forums, part of the General Programming Boards category; So I'm making a simple shooter game and I want to remove an element from my vector when it gets ...

  1. #1
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    About STL vector.erase

    So I'm making a simple shooter game and I want to remove an element from my vector when it gets killed, my question is what is the best way to do it?

    I've worked out that I can delete an object no problem using the Vector.erase (Vector.begin () + Collided); method where Collided is the index of the object I want to remove. However would this leave a big gaps in memory? I use the vector.size () functions to work out how many objects I should check for collisions so will this be reduced when i kill of one of my units?

    Is this the best way to store the information about my units?

  2. #2
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    >However would this leave a big gaps in memory?
    No.

    >Is this the best way to store the information about my units?
    Yeah.

  3. #3
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    Ok thanks! Now a couple more questions:

    Why does my code crash when i try to do this:

    In my game loop I load waves of enemies like this:
    Code:
    void Logic::LoadWaves (void)
    {
    	BlankCounter++;
    	if ((BlankCounter > 50) && (WaveCounter == 1))
    	{
    		enemies.AddEnemyToVector (2);
    		WaveCounter =2;
    	}
    }
    BlankCounter is the number of frames being rendered and enemies is my storage class for my vector. The AddEnemyToVector looks like this:

    Code:
    void EnemyList::AddEnemyToVector (int NumberToSpawn)
    {
    		for (int i = 2; i < NumberToSpawn; i++)
    	{
    	venemyVector.push_back (new Enemy); // add new unit to array
    	venemyVector[i]->SpawnEnemy (i); // spawn enemy unit
    	}
    }
    Number to spawn is the number of enemies to spawn per wave, this all works fine, however when i try to remove them like this:

    Code:
    void EnemyList::KillEnemy (int Collided)
    {
    	ExplosionX = venemyVector[Collided]->GetLeft ();
    	ExplosionY = venemyVector[Collided]->GetTop ();
    	
    	Boom.LoadGFX (); // load graphics for explosion
    	Boom.Bang ((ExplosionX - 16), (ExplosionY - 16)); // run animation
    	venemyVector[Collided]->Die (Collided); //make the unit explode
    	venemyVector.erase (venemyVector.begin () + Collided);  // erase unit from vector
    }
    Its the two bold lines at the bottom which aren't right, it sometimes works when i kill the last spawning unit first but sometimes one of the units remains when i call delete on it, it doesn't move or anything, i just get the random explosion when it collides with my player. Anyone got any ideas what it could be? Do I need to swap to the end of the vector before i delete it or something? If so what is the code to do that?

  4. #4
    Cat
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    When you use the vector throughout the code, do you access the vector elements sequentially or is there a need to access them in nonsequential order?

    If you're accessing sequentially, consider std::list<>. It'll almost certainly give you a performance boost, and if you have no need for nonsequential access, the only real benefit of vector<> over list<> is gone.
    You ever try a pink golf ball, Wally? Why, the wind shear on a pink ball alone can take the head clean off a 90 pound midget at 300 yards.

  5. #5
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    Quote Originally Posted by Cat View Post
    When you use the vector throughout the code, do you access the vector elements sequentially or is there a need to access them in nonsequential order?

    If you're accessing sequentially, consider std::list<>. It'll almost certainly give you a performance boost, and if you have no need for nonsequential access, the only real benefit of vector<> over list<> is gone.
    It has to be non-sequential since the game doesn't know which enemy the player will attack first, I think may be the problem in that the game as the units are being deleted then their numbers are changing? is there anyway to reorganise them somehow so that i only delete one from the end?
    Last edited by -pete-; 04-01-2007 at 02:10 AM.

  6. #6
    The larch
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    If the order of data in the vector doesn't matter, you can swap the one you want to erase with the last item and pop_back the vector.

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