Question

I am getting garbage in my user defined vector.Garbage comes after erase function this is the code

    #if 1   // Make it 1 to enable this code

#include <iostream>
using namespace std;

class Vector{
protected:
    int l;
    int* v;
public:
    Vector():l(0),v(0){
        cout << "\nBase class: Vector: Default constructor" << endl;
    }
    Vector( int len ):l(len),v(new int[l]) {
        cout << "Vector: Overloaded constructor" << endl;
    }
    void set( int i, int val)
    {
        if( l )
            v[i] = val;
        else{
            cout << "Error: zero size vector\n exiting..." <<endl;
            exit(5);
        }
    }
    int get( int i)
    {
        if( l )
            return v[i];
        else{
            cout << "Error: zero size vector\n exiting..." <<endl;
            exit(5);
        }       
    }   
    ~Vector(){
        cout << "Base dextructor" <<endl;
        delete [] v;
    }

};

class Vector1:public Vector{
private:

public:
    Vector1():Vector(){
        cout << "Derived class: Vector1:: Default constructor" << endl;
    }
    //my functions
    int size()
    {
    return l;
    }
    int front()
    {
    return Vector::get(0);
    }
    int end()
    {
    return Vector::get(l-1);
    }
    void swap(int a,int b)
    {
    int temp=v[a];
    v[a]=v[b];
    v[b]=temp;
    }
    void find(int val)
    {
        bool flag=false;
       for(int i=0;i<l;i++)
       {
         if(v[i]==val)
         {
         flag=true;
         }
       }
       if(flag==true)
           cout<<"\nValue ="<<val<<" =Exists in Vector";
       else
           cout<<"\nValue ="<<val<<" =doesnot Exists in Vector";
    }
    void erase(int val)
    {

        int *temp=new int[l-1];
        int k=0;
        for(int i=0;i<l;i++)
        {
        if(v[i]!=val)
        {
        temp[i]=v[i];
        k++;
        }
        }
        delete []v;
        l=l-1;
        v=new int[l];
        for(int i=0;i<l;i++)
        {
        v[i]=temp[i];
        }



    }
    int resize( int len ) 
    {
        if( l )
            delete [] v;
        l = len;
        v = new int[l];
        return (v!=0);
    }
    void set( int i, int val)
    {
        if( i>= 0 && i<l )
            Vector::set( i, val );
        else{
            cout << "Error: index out of range\n exiting..." <<endl;
            exit(3);
        }
    }
    int get( int i)
    {
        if( i>= 0 && i<l )
            return Vector::get(i);
        else{
            cout << "Error: index out of range\n exiting..." <<endl;
            exit(3);
        }
    }   
    int & operator [](int i)
    {
        return v[i];
    }

    Vector1( int len ):Vector(len)
    {

    }

};

int main()
{
    Vector vec; 

    Vector1 v1;
    v1.resize( 4 );
    v1.set( 2, 4);
    v1.set( 1, 5);
    v1.set( 0, 6);

    int x = v1[2];

    v1[3] = 77;
    cout<<"\nSize of vector is=\n"<<v1.size();
    //v1.set( 5, 4);        // erroneous value
    cout<<"\nFront of vector is=\n"<<v1.front();
    cout<<"\nEnd of vector is=\n"<<v1.end();
   //do swap between values
    cout<<"\n";
    v1.swap(1,3);
    //now values are
    cout<<"v1[1] is equals to= "<<v1[1];
    cout<<"v1[3] is equals to= "<<v1[3];
    v1.find(5);
    v1.find(100);
    cout<<"\nNow v1[0] is equals to= \n"<<v1[0];
    v1.erase(6);
    cout<<"\nNow v1[0] is equals to= \n"<<v1[0]<<"  "<<v1[1];
    cout<<"\n";
}
#endif

Output is this

v1[0] should be be 5

Answer 1

In your erase function, you are not actually erasing the given number, you just copy every number in the vector that is not equal to the given number to a new array. E.g., if your internal array in the vector contained the numbers 2, 4, 6 and 8, and you are erasing 6, you just copy 2, 4 and 8 into a new array into indices 0, 1 and 3, while keeping slot 2 in the new array as undefined. Then you make a third array that is one shorter than the new array, and copy everything except the last item into the third array, including the undefined slot 2, but not the last slot (which should have been kept).

I think that using temp[k] = v[i] would solve your problem in the erase function, but note that it still won’t be a perfect solution because the item being deleted might occur multiple times in the vector, or it might not be there at all, so it is not always the case that the new length is one smaller than the old length.