Question

I have a segmentationfault at the line :

cout <<  b[0][0];

Could someone tell me what should I do to fix my code?

#include <iostream>
using namespace std;

int** gettab(int tab[][2]){
   return (int**)tab;
}

int main() {
   int a[4][2] = {{0, 0}, {1, 0}, {2, 0}, {2, 1}};
   int ** b = gettab(a);
   cout <<  b[0][0];
   return 0;
}

Answer 1

A 2-dimensional array is not the same thing as an array of pointers, which is how int** is interpreted. Change the return type of gettab.

int* gettab(int tab[][2]){
   return &tab[0][0];
}

int main() {
  int a[4][2] = {{0, 0}, {1, 0}, {2, 0}, {2, 1}};
  int* b = gettab(a);
  cout << b[0]; // b[row_index * num_cols + col_index]
  cout << b[1 * 2 + 0]; // the 1 from {1, 0}
}

Or:

int (*gettab(int tab[][2]))[2] {
  return tab;
}
// or:
template<class T> struct identity { typedef T type; };
identity<int(*)[2]>::type gettab(int tab[][2]) {
  return tab;
}

int main() {
  int a[4][2] = {{0, 0}, {1, 0}, {2, 0}, {2, 1}};
  int (*b)[2] = gettab(a);
  cout << b[0][0];
}