Creating a 2D Array of a Class C++ - c++

Question

I'm using a C++ engine called libtcod to print out ASCII characters in a rogue-like game.
In the game I want to represent the 'map' as a 2D array of type Map, which contains 'layer1' for tiles, e.g Grass, Sand, Water, and a second layer to represent objects on top of layer2, e.g Trees and Boulders.
I have created the Map class, which contains two attributes; one of type Tile, and the other of type Object.
However I seem to be having difficulties in the creation of the 2D array itself.
I am getting the error: "an array may not have elements of this type"
#include "libtcod.hpp"
#include <ctime>
#include <stdio.h>
#include <ciso646>
#include <cstring>
static const TCODColor colour_darkWall(128, 128, 128);
static const TCODColor colour_grass(0, 255, 0);
static const TCODColor colour_black(0, 0, 0);
static const TCODColor colour_white(255, 255, 255);
static const TCODColor colour_blue(0, 0, 255);
static const TCODColor colour_brown(139, 69, 19);
static const TCODColor colour_red(255, 0, 0);
int i, j;
class object {
public:
char name[20];
TCODColor colour;
char symbol;
bool passable;
object(int layer_id) {
if (layer_id == 0) { //EMPTY
strcpy(name, "NA");
symbol = ' ';
passable = true;
colour = colour_white;
}
else if (layer_id == 1) { //TREE
strcpy(name, "Tree");
symbol = '^';
passable = false;
colour = colour_grass;
}
else if (layer_id == 2) { //ROCK
strcpy(name, "Rock");
symbol = 'R';
passable = false;
colour = colour_black;
}
}
};
class tile {
public:
char name[20];
TCODColor colour;
bool passable;
tile(int layer_id) {
if (layer_id == 0) { //WATER
strcpy(name, "Water");
colour = colour_blue;
passable = false;
}
else if (layer_id == 1) { //GRASS
strcpy(name, "Grass");
colour = colour_grass;
passable = true;
}
else if (layer_id == 2) { //SAND
strcpy(name, "Sand");
colour = colour_brown;
passable = true;
}
}
};
class Map {
public:
tile layer1;
object layer2;
Map(int layer1_id, int layer2_id) {
layer1 = tile(layer1_id);
layer2 = object(layer2_id);
}
};
int main() {
const int window_x = 150;
const int window_y = 50;
Map[][] map = new Map[5][5];
TCODConsole::initRoot(window_x, window_y, "CivSim v0.1", false);
while (!TCODConsole::isWindowClosed()) {
TCODConsole::root->clear();
TCODConsole::root->putChar(0, 0, map.layer2.symbol);
TCODConsole::flush();
}
return 0;
}
Not sure how to create the 2D array in question.
Thanks in advance for any help!

Answer 1

Map[][] map = new Map[5][5]; is not legal. Only the first dimension can be omitted. You need Map[][5] map = new Map[5][5]; or better still Map (*map)[5] = new Map[5][5];.
The reason is that these notations using [] in a type are just another (and confusing) way of describing a pointer type. So int[] x is just a different way of writing int* x and Map[][5] m is just another way of writing Map (*m)[5] (which is to say a pointer to an array of five Maps).
I think you should always use the pointer version of these notations, it's more correctly describes what you are really doing. In the long term writing code that looks like you have an array, when all you actually have is a pointer is confusing.
So why isn't Map[][] another way of writing Map**? It's because the similarity between arrays and pointer in C and C++ only works for one level. A two dimensional array is a fundamentally different structure from a pointer to an array of pointers. So int[5][5] isn't compatible with int** so there is no reason to make int[][] mean the same as int**.