vector template ?

This is a discussion on vector template ? within the C++ Programming forums, part of the General Programming Boards category; What does the vector class do if you give it a NULL pointer. Does it still add that to the ...

  1. #1
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    vector template ?

    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?

  2. #2
    pronounced 'fib' FillYourBrain's Avatar
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    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.

  3. #3
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    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.

  4. #4
    Shadow12345
    Guest
    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!
    Last edited by Shadow12345; 09-02-2002 at 09:53 AM.

  5. #5
    ¡Amo fútbol!
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    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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