Delete and add elements to vector inside main loop

Question

I searched before but couldn't find any answers. I am somewhat new to c++, so hopefully this question won't be too stupid. I am trying to add and remove elements in a vector, in my case populated with particles during a big update or drawing loop over all particles. For example remove some particles because they died, but also add a few other ones because one particle collided with an object and I want to show a small particle burst at the point of collision. I made this simple test code in a demo file to get to the bottom of the problem. I think the problem is since I delete and add particles the iterator pointer becomes invalid. Deletion works, but when I add a few random ones I get a null pointer. the code below is somewhat verbose, I know I should use iterators with begin() and end() but I had the same problem with those, and played with the code a bit, trying more javascript array style looping because I am more familiar with that. ``` void testApp::drawParticles() { int i=0; int…

Accepted Answer

Every time you insert in to a `vector`, the iterators to it are potentially invalidated. You cannot do this:

```
if ( ofRandom(1) < .1 ) addSomeNewOnes();
it++
```

Because after the call to `addSomeNewOnes()`, `it` is invalid.

You can use the iterator returned by a call to `vector::insert`, but in your case that would mean re-engineering your code.

This is something you might want to do, anyway, as your code is a bit kludgy.

Delete and add elements to vector inside main loop

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