Question about vectors

[Mythios]

Hey guys,

Just wondering how i would go about this problem. As you see I'm filling up a vector with objects of a struct knight. But I'm not sure how to get each object in the vector and give it a random value.

So basically I'm not sure how you call the object in the vector for giving it a value.

#include <iostream>
#include <vector>

struct Knight{
	int health;
	int armour;
	int damage;
};

int main()
{
	Knight *player = new Knight;
	std::vector<Knight> *myKnightsOne = new std::vector<Knight>;
	std::vector<Knight>::iterator *myKnightsIterator = new std::vector<Knight>::iterator;

	for(int i = 0; i < 20; i++)
	{
		myKnightsOne->push_back(*player);
	}

	for(*myKnightsIterator = myKnightsOne->begin(); *myKnightsIterator != myKnightsOne->end(); *myKnightsIterator++)
	{
		//myKnightsOne->begin()->armour;
		//How can i fill up the values here using vectorObject->damage = rand() % 50; Etc
	}

	return 0;
}

[jsmith]

Why not make a constructor for Knight that does that for you?

Second, why are you dynamically allocating the vector and the iterator? It just makes use of both that much harder.

Otherwise in your code you need to do:

for( *myKnightsIterator = myKnightsOne->begin(); 
      *myKnightsIterator != myKnightsOne->end();
      ++*myKnightsIterator )
{
    (*myKnightsIterator)->armour = rand() % 50;
}

[Mythios]

Cheers mate, hey i wouldn't do it all like this if I didn't have to. I'm currently a student at Atari so they are big on memory management. I'm partially new to c++ as well but just following the guide lines lol

[jsmith]

<sarcasm> Apparently so... make the programmer manage memory as much as possible. That will result in robust, error-free code.</sarcasm>

<empathy>I'm sorry to hear that.... in that case the above code should work (I did not even compile).</empathy>

[Mythios]

...

[jsmith]

I just looked at the code a little more closely and it seems you are doing more typing than you need to.

std::vector<Knight> *myKnightsOne = new std::vector<Knight>( 20, Knight() );

would create a vector of 20 default constructed Knight elements without the need for the first for() loop.

[Mythios]

Lol, cheers for that mate. Awesome :D

[Mythios]

One other question, say one of the knights in the vectors health equaled zero, is it possible to remove the knights health that equals zero from the vector. Or can you only remove and add elements from the end and front etc

And see how you did this

(*myKnightsIterator)->armour = rand() % 50;

Why is the iterator in brackets here?

Thanks

[jsmith]

Q1: Yes, you can, although if you intend to remove elements from the vector that are not at the very end, then a vector might not be best the choice, because deletes anywhere other than the last element are very expensive. vector<> has an erase( iterator ) method that you can use.

Q2: Normally you use -> to dereference the iterator to get at the referenced item. Hence the -> above. But your myKnightsIterator variable is a pointer to an iterator, hence we have to dereference the pointer to get at the iterator first. So essentially you need two dereferences: the first to get to the iterator and the second to get at the item. This syntax isn't legal: myKnightsIterator->->armour; so we have to use *. So (*myKnightsIterator) dereferences the pointer to get to the iterator, and then -> dereferences the iterator to get to the item.

I'm not sure if the parens are needed. If it compiles without them, then you don't need them. I put them in because I know it will work that way (I have not tried to compile anything).

It's a bit strange to declare a pointer to an iterator, hence my original comment. Doing so leads to the above messy syntax, and it doesn't really save anything because sizeof(std::vector<>::iterator) is either very close to sizeof( std::vector<>::iterator*) or equal to it (iterators are lightweight).

[Mythios]

Cheers for that mate, but this is just a very small test program as well so it won't be much bigger than a good 100 lines. But thanks a heap for your input it's helped a lot :)