Access fields of a struct dynamically

Question

I have defined these 2 structs:

#define MAP_SIZE 5

typedef struct battle_cell {
  int status_a;
  int status_b;

  int ship_a;
  int ship_b;
} battle_cell;

struct battlemap {
  battle_cell cell[MAP_SIZE][MAP_SIZE];
  int progress_a;
  int progress_b;
};

After the initalization of the map and all the other variables with zeros:

for (i = 0; i < MAP_SIZE; i++) {
  for (j = 0; j < MAP_SIZE; j++) {
    map->cell[i][j].status_a = 0;
    map->cell[i][j].status_b = 0;
    map->cell[i][j].ship_a = 0;
    map->cell[i][j].ship_b = 0;
  }
}

map->progress_a = 0;
map->progress_b = 0;

There is a point that I have to check the ship_a and ship_b values that live in each cell, something like that (the logic is a bit more complex than this iteration):

for (i = posXB; i < posXB + SHIP_SIZE; i++) {
  map->cell[posYB][i].ship_b = 1;
}

I need to do exactly the same for the ship_a variable. So, I have to duplicate quite a big chunk of code because I am not able to find a way to get the field within the struct dynamically. For example, I could define a function:

void cell_iteration (battlemap *map, int pos, int pos_y, int ship_size, /* field_parameter/pointer */) {
  int i;
  for (i = pos; i < pos + ship_size; i++) {
    map->cell[pos_y][i].ship_b = 1; // use the field_parameter/pointer instead of ship_b
  }
}

Is there an elegant way to do something like that?

UPDATE

Just a clarification. The structs can definitely be simplified, but this is not my question. I 've just tried to create an example :)

You can probably simplify the data structure. Maybe you could define a ship structure that contains the position(s) of a ship, rather than put so much inside the battle_cell struct. — Stuart
– Stuart, Commented Oct 6, 2016 at 18:49
@Stuart definitely the structs can be simplified and this is what the guy below answered. I 've tried to simulate a complicated case just to give an example. I think that I have to edit the question to clarify this :) — Stavros Zavrakas
– Stavros Zavrakas, Commented Oct 6, 2016 at 18:53
I'm probably not understanding your question because I don't see how creating an array[2] of ships inside battle_cell helps you. I'm thinking that instead of a field parameter pointer you just need a parameter that indicates which ship you want to access and then have the code access either or maybe both ships. — Stuart
– Stuart, Commented Oct 6, 2016 at 19:00
I don't know what you mean by "access dynamically the properties of the struct". — Stuart
– Stuart, Commented Oct 6, 2016 at 19:02
@Stuart Defining an array[2], you can make an assumption that the 0 position will be ship_a and position 1 will be ship_b. Then you can pass simple integer 0 and 1 and will be able to access the fields (at least this is what I understood). I am not 100% sure if I understood your suggestion, though. Is it possible to create a very small snippet and post it as an answer? — Stavros Zavrakas
– Stavros Zavrakas, Commented Oct 6, 2016 at 19:08

Jean-Claude Colette · Accepted Answer · 2016-10-06 18:37:21Z

3

Instead if ship_a and ship_b int the first struct, you can declare int ship[2] an array of 2 int.

answered Oct 6, 2016 at 18:37

Jean-Claude Colette

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2 Comments

Stavros Zavrakas Over a year ago

This is a solution that can work, but I would really like to know if there is a way to access dynamically the properties of the struct.

Tony Tannous Over a year ago

I thought the compiler is smart enough to do this on his own.

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