CODEWITHSUNDEEP
c++arrayspointers
diego9403
diego9403

Reputation: 153

C++ 2d array created by double pointer

I want to create 2d array using pointer and show then show it. I change rows by increment pointer (one *) and columns by index. My code:

int ** tabl=new int *[4];
for (int i=0;i<10;i++)
    tabl[i]=new int [3];
int **ptab=tabl;//save first position of array

for (int i=0;i<4;i++)
{
    for (int j=0;j<3;j++)
    {
        *tabl[j]=rand()%10 +1;
        printf("%4d",*tabl[j]);
    }
    tabl++;
}
tabl=ptab;
cout<<endl<<endl<<endl;
for (int i=0;i<4;i++)
{
    for (int j=0;j<3;j++)
    {
        printf("%4d",*tabl[j]);
    }
    tabl++;
}

Output:

   2   8   5   1  10   5   9   9   3   5   6   6

   2   1   9   1   9   5   9   5   6   5   6   6

But some of the digits in the second loop are different then the original. Why?

Upvotes: 0

Views: 67

Answers (1)

Ishamael
Ishamael

Reputation: 12795

The problem is the way you refer to the element. It should be (*tabl)[j], not *tabl[j].

Also note that you go beyound allocated memory here:

int ** tabl=new int *[4];
for (int i=0;i<10;i++)
               ^
    -----------+

Upvotes: 5

Related Questions