Vector of Objects = crash and burn

[Vandrian]

I want to...
1) make a simple class Object that stores some integers etc...
2) put this Object class into a vector
3) Loop through the vector and call the class member function stats() which prints info the Object is storing.

I have tested Object and it should work fine my problem is getting classes into the vector and then dereferencing the function stats. Any help greatly appreciated I don't think this should be that difficult, but I don't know the answer.

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

class Object
{
  public:
    int mCurPosX;
    int mCurPosY;
    
    int mNewPosX;
    int mNewPosY;
    
    int mSymbol;  //integer that will be cast to a character when printed
    
    static int sNumObjects;
    
    Object(int curPosX, int curPosY, int symbol);
    void stats();
};

int Object::sNumObjects = 0;

Object::Object(int curPosX, int curPosY, int symbol)
{
    mCurPosX = curPosX;
    mCurPosY = curPosY;
    mSymbol = symbol;
    
    mNewPosX = mCurPosX;
    mNewPosY = mCurPosY; 
    
    ++sNumObjects;   
}

void Object::stats()
{
    cout << "=========== Object " << this << " Stats ===========\n";
    cout << "mCurPosX = " <<  mCurPosX << endl;
    cout << "mCurPosY = " <<  mCurPosY << endl;
    cout << "mSymbol = " << mSymbol << "\n\n";
    
    cout << "mNewPosX = " <<  mNewPosX << endl;
    cout << "mNewPosY = " <<  mNewPosY << "\n\n";
    
    cout << "Total Number of Objects = "<< sNumObjects << endl;
}


//#########################################
//                          PROBLEM AREA BELOW
//#########################################

int main()
{   
    vector<Object*> pVectorObj;
    
    for(int i=0; i<=10; ++i)
    {
        Object* temp = new Object(0,0,97);
        pVectorObj.push_back(temp);
    }
        


    for(vector<Object*>::const_iterator iter = pVectorObj.begin();
        iter != pVectorObj.end(); ++iter)
    {
        cout << "iter = " << *iter << endl;

        //produces error iter->.stats();                        //#############
        //error: stats not declared *iter.stats();
        //error: stats not declared *(*iter).stats();

    }
    
    cout << "pVectorObj.size() = " << pVectorObj.size() << endl;
    
    
    system("pause");
    return 0;   
}

[Daved]

If you're holding pointers in your vector, you must dereference the iterator and the pointer. I would do it this way:

(*iter)->stats();

However, I don't see a reason to hold pointers in your vector. Why not just use vector<Object>? If you made that switch then you wouldn't have to worry about potential memory leaks like the one your program has now.

[Vandrian]

I was really banging my head on that one. The reason I was trying to use pointers was because (I didn't get the Object vector to work either), and also my book that I am learning from used pointers instead of a vector of objects.

Thanks again!

[Daved]

>> I didn't get the Object vector to work either.
I'd highly recommend focusing on getting that to work:

    for(int i=0; i<=10; ++i)
    {
        pVectorObj.push_back(Object(0,0,97));
    }

    // ...

        iter->stats();

[Vandrian]

I wasn't able to get it to work. This is what main looks like (I haven't changed the class Object). Also something else I don't understand is that it prints stats() now no matter what and it isn't in the constructor.

int main()
{   
    vector<Object> vectorObj;
    char userInput = 'n';
    
    for(int i=0; i<=10; ++i)
    {
        vectorObj.push_back( Object(i,i,97));
    }
    
    cout << "Print stats from vectorObj? y n :" << endl;
    cin >> userInput;
    
    if( userInput == 'y')
    {
        for(vector<Object>::const_iterator iter = vectorObj.begin();
            iter != vectorObj.end(); ++iter)
        {
            
            iter->stats();
            // passing `const Object' as `this' argument of 
            // `void Object::stats()' discards qualifiers 
                    
        }
    }

    cout << "vectorObj.size() = " << vectorObj.size() << endl;
    
    
    system("pause");
    return 0;   
}

[dudeomanodude]

I suspect part of your problem lies here:

 for(vector<Object*>::const_iterator iter = pVectorObj.begin();

You must be getting compiler errors, what are they telling you?

Hint: Pressing the delete key 6 times within that line will do the trick.

EDIT: I should offer the alternative as well:

adding "const" to stats() in it's definition and prototype will work as well:

class Object{

    void stats() const;

    //...
};

void Object::stats() const{

}

You need to either make stats() return constant, if you want a constant object to call it, or just use a regular iterator and leave stats() alone:

class Object{

  void stats();
  //...
};

void Object::stats(){

}

int main(){

    vector<Object> my_vec;
    //...
    vector<Object>::iterator iter = my_vec.begin();    // NOTE: The use of regular iterator here
    //...
    return 0;
}