Why does my loop iterate only twice?

Question

I have defined two structs and when I loop to set their values, it only loop twice as printf return. Any ideas?

typedef struct {
  int x;
  int y;
  unsigned char status;
} Cell;

typedef struct {
  int sizeX;
  int sizeY;
  Cell cell[];
} World;

int main() {
  int i, x, y;
  i = 0;
  World grid;
  grid.sizeX = 10;
  grid.sizeY = 10;

  for (x = 0; x < grid.sizeX; x++) {
    for (y = 0; y < grid.sizeY; y++) {
      Cell cell;
      cell.x = x;
      cell.y = y;

      printf("%d,%d: ", cell.x, cell.y);

      grid.cell[i] = cell;
      i++;
    }
  }

    return 0;
}

---

EDIT :

Correct answer given below, thanks for comments and your patience for a C noob !

Answer 1

grid.cell[] is not have been allocated any memory space. You should allocate it a memory by adding following line before starting of the loop:

 grid.cell = Cell[100];

The size 100 is based on the fact that grid.sizeX = 10; and grid.sizeY = 10; . There is no need of using malloc() because the size is fixed.

If size is not fixed for grid.sizeX and grid.sizeY then, you should add following line instead of grid.cell = Cell[100]; :

 grid.cell = (Cell*)malloc(sizeof(Cell) *(grid.xSize  * grid.ySize ));

The line World *grid = malloc(sizeof(World) + xSize * ySize * sizeof(Cell)); which is added by you is just a tricked way and not much clear. Even it is logically correct!!!

Answer 2

Your World struct has a flexible array member as the last element. There is actually no space set aside for that member. As a result, you write off the end of the struct when you write to the array, resulting in undefined behavior.

You need to declare a World * and use malloc to allocate space for the struct plus the array.

World *world = malloc(sizeof(World) + 10 * 10 * sizeof(Cell));

Answer 3

Here is the results :

#include <stdio.h>
#include <stdlib.h>
#define LIVE 1
#define DEAD 0
#define xSize 10
#define ySize 10

typedef struct {
  int x;
  int y;
  unsigned char status;
} Cell;

typedef struct {
  int sizeX;
  int sizeY;
  Cell cell[1];
} World;

int main() {
  int i, x, y;
  i = 0;
  World *grid = malloc(sizeof(World) + xSize * ySize * sizeof(Cell));;
  grid->sizeX = xSize;
  grid->sizeY = ySize;

  for (x = 0; x < grid->sizeX; x++) {
    for (y = 0; y < grid->sizeY; y++) {
      Cell cell;
      cell.x = x;
      cell.y = y;
      cell.status = DEAD;

      printf("%d,%d: ", cell.x, cell.y);

      grid->cell[i] = cell;
      i++;
    }
  }

    return 0;
}