C++ Shifting array of pointers to structures

Question

The function is OK now, topic achieved. Thanks everyone.

I have the following very simple structure inside the class:

struct Data
{
    string name1;
    string name2;
    string name3;
    string name4;
}

I initialize:

Data **data;
data=new Data*[size];

The problem is to shift all the pointers to the elements of array from the position N to the right , so that I can insert a new element into N. I've tried various things, but everything ended up with an array of elements pointing to the same object...

I have the similar function which deletes the element and shifts everything to the left. It's working fine:

int Del_element(/*some parameters*/)
{
    found=Bin_search(Name1,Name2); //binary search. Returns index of element.
    if (found<0) return 0; //element wasn't found

    delete data[found]; //delete pointer
    for (int i=found; i<index-1; i++) //shift all pointers to the left
    {
        data[i]=data[i+1];
    }
    index--;
    return 1;
}

The function which I implemented is below:

void re_size() 
{
int size_old=size;
size*=2;
Data **tmp_array;

tmp_array = new Data*[size];

copy(data, data+size_old, tmp_array);
delete []data;
data=new Data*[size];
data=tmp_array;
}



 int Add( const string & Name1,const string & Name2,const string & Name3, const string & Name4 )
    {
        int found=Bin_search(Name1,Name2); //binary search. Return positive number if found, or negative as the position to insert new element;

  if (found>0)  //if element already exists
  {
      return 0;
  }


if ((index+1)==size) {re_size();}

data[index]= new Record(Name1,Name2,Name3,Name4);
if (index>0)
{
  for (int i=index; i>-found; i--)
  {
   *data[i]=*data[i-1];
  } 

  data[-found]->name1=Name1;
  data[-found]->name2=Name1;
  data[-found]->name3=Name1;
  data[-found]->name4=Name1;
}

 index++; 
 return 1;
}

Basically, I initialize new element at the end of array, then copy elements from the end of array to found position and copy values into data[-found].

Answer 1

You didn't show the non-working code, so I'll have to guess what you did wrong.

I'll bet you shifted element 0 into 1, 1 into 2, 2 into 3, etc. But when you shift 1 into 2, it contains what was originally in 0. And then when you shift 2 into 3, it contains what you just shifted from 1, which was originally in 0. And so on.

You need do the shifts starting from the end: N-1 into N, N-2 into N-1, N-3 into N-2, etc.

The fact that the things you're shifting are pointers is completely irrelevant, you'd have the same problem with an array of numbers.

Answer 2

First, Del_element function is here to delete an element for new incoming pointer. If is it true, then it doesn't work because you just occupy freed element ( data[first] ) with new one ( data[first+1] ).

But if, you should be sure if you mean N equals to size and new incoming pointer must be places in size, it's OK.

However, you must show real and more complete code.

OK, that's better. First of all I think it is not so good to return false in the function with int return type. Second, I feel there is a big problem here for (int i=index-1; i>-found; i--) . Why i>-found ?