CODEWITHSUNDEEP
vectorstliterator
user2213764
user2213764

Reputation:

Using STL iterators with vectors

Hello I'm trying to access an element of a vector containing a bunch of class objects and delete only one of the objects from the vector.

The problem is I don't understand vectors and I can't find any information online which is helpful.

My code:

void MyExperiment::deselectSingle() {
Ogre::Vector3 vNewPos = mPickedObj->_getDerivedPosition();
mPickedObj->showBoundingBox( false );
mMoveThis->removeChild( mPickedObj->getName() );
mSceneMgr->getRootSceneNode()->addChild( mPickedObj );
mPickedObj->_setDerivedPosition( vNewPos );

for ( Ogre::SceneNode* it = vObjects.begin(); it < vObjects.end(); it++ ) {
    static std::string objNameStr;
    objNameStr = vObjects.at( *it  )->getName();
    if ( objNameStr == mPickedObj->getName() )
    {
        vObjects.erase( *it );
        break;
    }
}
if ( mMoveThis->numAttachedObjects() == 0 ) bSelected = false;
return;

}

I know this code won't work. I've read some stuff online about how to use iterators however when I try some of the things suggested errors crop up. In fact what I have here causes a few errors.

My plan for this function was to iterate through the vObjects vector which contains Ogre::SceneNode pointer elements. If one of the elements matches the mPickedObj's name then I want to remove it from the vector by the .erase() foo. The code above does not work, it was just there as an example though it is what I tried in my application.

Upvotes: 0

Views: 101

Answers (2)

Dineshkumar
Dineshkumar

Reputation: 4245

you are initializing the vector in rightway before forloop; but in initialization part of for loop: why reinitialized it again?

Ogre::SceneNode* it = vObjects.begin()

Iterator 'll be initialized to begin() [first element] and loops through its item until it reaches end.

 (it=vObjects.begin();it!=vObjects.end();it++)

you should not compare it normally with ' < ' operator. it ends when it reaches end [i.e end position exclusive]

i'm not sure what is vObjects.erase(*it) ...

But if you want to dereference an element in vector do 

vector[i] //if ith element already present if not it causes segmentation fault [can use it like normal array]
vector.at(i)  //safe and if doesn't exist throws exception

for deleting an element you pass the iterator position for erase(it) to delete it; if element is at last can use pop_back().

Upvotes: 0

gbjbaanb
gbjbaanb

Reputation: 52689

What a vector is.

A beginner's tutorial on vectors

Not too hard at all - take the time to understand the STL collections, and you'll have a resource that fits for 80% of the things you need in the future.

The only 'special' thing you need to know for a vector, as opposed to the other collections, is that erasing an element in the middle of a vector will cause the rest of the elements to move down to close the gap you just made.

Upvotes: 1

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