C++ how to display multidimentional array in OO design - c++

Question

Hi I'm writing a simple version of Pacman with OO design in C++. I have problem displaying the content of a 2D array. The array constains a bunch of symbols, which represent the wall of the map/maze. Here is the sample code that I wrote:
Game.h
class Game
{
private:
char map;
public:
Game();
void displayMap();
};
Game.cpp
char map[10][20] = {...};
void Game::displayMap()
{
for(int i = 0; i < 10; i++)
{
for(int j = 0; j < 20; j++)
{
cout << map[i][j] << " ";
}
cout << endl;
}
}
The compiler will pop out an error at [i] saying "expression must have pointer-to-object type".
But if I define the size of the array in the header file and assign its value when defining the constructor
Game.h
class Game
{
private:
char map[10][20];
};
Game.cpp
Game::Game()
{
char map[10][20] = {...};
}
It will compile but when I try to display the content of the array (using the same code of displayMap()), I found out it's filled with junk. I think it's because that assignment is not an assignment. It's actually an initialization of another array on the stack, so that array is destroyed after the constructor finishes, and the displayMap() at that time display the original unassigned array.
I could be wrong, so feel free to correct me. I need a recommendation on how should I structure my game to avoid this problem

Answer 1

Game::Game() {
char map[10][20] = {...};
}
Here you redeclare a local variable with the same name of the instance variable, hence you hide the outer one. In addition you are trying to assign to an array which has been declared before, that's not possible in C++. You can just initialise an array when you declare it, not afterwards.
You can do this (if you have C++11 support):
class Game {
char map[W][H] = { ... };
}
or you can do this:
class Game {
char map[W][H];
Game() {
char tmp[W][H] = { ... };
memcpy(map, tmp, sizeof(char)*W*H);
}
}
Even better, you can use std::copy. Or even even better just use an std::array and forget normal arrays.

Answer 2

I commented your question, but I think it would be good to make it an answer, so here it is.
The second option should work fine.
Garbage values are normal in C/C++.
What you have to do is to initialize your values inside your constructor ( Game::Game() ). Constructors are meant to be used in these cases.
The behavior of C/C++ is to not assign a default value, it just "takes what's in place in RAM". Other languages do initialize the RAM cells though. It all depends of what programming language you are using.
Including this code inside your constructor (before accessing map[][] for another thing) should work:
for (int ix = 0; ix < 10; ix++)
for (int jx = 0; jx < 20; jx++)
map[ix][jx] = "x"; // x will be your default value