vector template ?

**Traveller** · 09-02-2002

What does the vector class do if you give it a NULL pointer. Does it still add that to the array? And if so you can derive from this class correct?

**FillYourBrain** · 09-02-2002

I think you mean void pointer (I could be wrong). As in:

vector<void *> v;

this basically allocates an array of void *s Nothing wrong with that. but if you meant:

vector<void> v;

I have no idea what to tell you. Another possibility (since you said NULL pointer):

vector<SomeClass *> v;
v.push_back(NULL);

This is just fine as NULL is valid to store in a SomeClass *.

Since the second choice seems the wackiest I'm sure that's it. vector<void> v; looks quite pointless but the best I can say is try it out in the compiler if you really want to know. I'm too lazy to test it myself right now.

**Traveller** · 09-02-2002

Sorry, I'll try to be more specific. In the program I'm using I utilize the vector class and in some instances my algorithm will return a NULL pointer if it does not intend to generate an object at the time. However the way it works is

Code:

vector<SomeClass*> SC;

SC = blah();

blah(){

     if (somecondition){
                  return new(SomeClass());
     }else
            return NULL;
}

I was wondering if this was taking up space in my vector array if blah returned NULL. Also if someone knows another way to do this, suggestions are always welcome.

Shadow12345 · 09-02-2002

I would say that yes it does

Code:

#include <vector>
#include <iostream>
using namespace std;

class Poop{
public:
	Poop() {}
private:
};

vector<Poop*> SC;

int main(void) {
	SC.push_back(NULL);
	cout << "SC[0] takes up " << sizeof(SC[0]) << " bytes" << endl;
	return 0;
}

Output:
The size of SC[0] is 4 bytes

EDIT:
I thought the size of a class was supposed to be all of its methods and variables added together. I changed the Poop class to this:
class Poop{
public:
Poop() {}
int GetHowManyPoops(){return HowManyPoops;}
private:
static int HowManyPoops;
long HowPoops;
double PoopsManyHow;
short ManyPoops;
double Crap;
double Cheese;
double ScrazzleFrazzle;
};

...BUT IT STILL SAYS IT IS ONLY 4 BYTES...THAT ISN'T CORRECT!

**golfinguy4** · 09-02-2002

You are getting the size of the address of the class, not the actual class. To get the size of the class, do sizeof(Poop).

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vector template ?