pointers and multi dimensional arrays

[adam2016]

Hi guys I'm trying to grasp the concept of how pointers work with multi dimensional arrays but I'm finding it hard,

I know this code will get the value of whats in the single dimensional array by dereferencing it

  int a[2];
  cout << *(a+2);

this will print out the last result in the array a which is a garbage value BUT

  int b[2][2];
  cout << *(b+2);

how come when I use the dereference operator on this expression it actually prints out a memory address not the actual value of b+2

thanks

[gunnerfunner]

how come when I use the dereference operator on this expression it actually prints out a memory address not the actual value of b+2

since b is a 2 * 2 matrix its 2 rows are at b[0] and b[1], so b+2 is not a valid memory address. In general for pointer representations of 2D arrays think about the memory allocation first in terms of the rows and then for each row in terms of it's columns, something along the line of the following program:

#include <iostream>

int main()
{
    int b[2][2] {{1,2},{3,4}};

    int* firstRow = b[0];
    int* secondRow = b[1];

    int* firstRowfirstCol = firstRow;
    int* firstRowsecondCol = firstRow + 1;

    int* secondRowfirstCol = secondRow;
    int* secondRowsecondCol = secondRow + 1;


    std::cout << "Element (0,0): " << *firstRowfirstCol << '\n';
    std::cout << "Element (0,1): " << * firstRowsecondCol << '\n';
    std::cout << "Element (1,0): " << *secondRowfirstCol << '\n';
    std::cout << "Element (1,1): " << *secondRowsecondCol << '\n';
}

[adam2016]

thanks gunnerfunner =)