Passing 2D arrays to function - c++

Question

I am trying to make an ASCII world, however I am unable to pass 2D arrays between functions. It is a 20 x 20 array, and I want to place houses randomly across it. The array won't pass like I want it to, and my tutorial told me that global variables are evil, so a solution without those would be great.
using namespace std;
void place_house(const int width, const int height, string world[width][length])
{
int max_house = (width * height) / 10; //One tenth of the map is filled with houses
int xcoords = (0 + (rand() % 20));
int ycoords = (0 + (rand() % 20));
world[xcoords][ycoords] = "#";
}
int main(int argc, const char * argv[])
{
srand((unsigned)time(NULL));
const int width = 20;
const int height = 20;
string world[width][height];
string grass = ".";
string house = "#";
string mountain = "^";
string person = "Å";
string treasure = "$";
//Fill entire world with grass
for (int iii = 0; iii < 20; ++iii) {
for (int jjj = 0; jjj < 20; ++jjj) {
world[iii][jjj] = ".";
}
}
place_house(width, height, world);
for (int iii = 0; iii < 20; ++iii) {
for (int jjj = 0; jjj < 20; ++jjj) {
cout << world[iii][jjj] << " ";
}
cout << endl;
}
}

Answer 1

Try passing string ** instead of string[][]
So your function should be declared like this:
void place_house(const int width, const int height, string **world)
and then you access your array usual way.
Remember to handle bounds correctly (probably you want to pass them together with array).
edit:
This is how you might achieve what you need:
#include <string>
#include <iostream>
using namespace std;
void foo (string **bar)
{
cout << bar[0][0];
}
int main(void)
{
string **a = new string*[5];
for ( int i = 0 ; i < 5 ; i ++ )
a[i] = new string[5];
a[0][0] = "test";
foo(a);
for ( int i = 0 ; i < 5 ; i ++ )
delete [] a[i];
delete [] a;
return 0;
}
edit
Another way of achieving what you want achieve (that is passing static array to a function) is to pass it as one dimmensional array and then use C-like way of accessing it.
Example:
#include <string>
#include <iostream>
using namespace std;
void foo (string *bar)
{
for (int r = 0; r < 5; r++)
{
for (int c = 0; c < 5; c++)
{
cout << bar[ (r * 5) + c ] << " ";
}
cout << "\n";
}
}
int main(void)
{
string a[5][5];
a[1][1] = "test";
foo((string*)(a));
return 0;
}
This little example is nicely described here (see Duoas post).
So I hope this will describe different ways of doing similar thing. This, however, does look quite ugly and probably is not the best programming practice (I would do everything to avoid doing that this way, dynamic arrays are quite nice you just need to remember releasing them).

Answer 2

Since your array has compile-time known dimensions, you could use templates to detect it like this:
template <std::size_t W, std::size_t H>
void place_house(string (&world)[W][H])
{
int max_house = (W * H) / 10; //One tenth of the map is filled with houses
int xcoords = (0 + (rand() % 20));
int ycoords = (0 + (rand() % 20));
world[xcoords][ycoords] = "#";
}
// ...
place_house(world); // Just pass it
Note, that this trick will not works with dynamically allocated arrays. In that case, you should use something like std::vector.

Answer 3

You don't need to size the parameter in the declaration and can't because the [][] syntax requires compile time constants.
Replace with string world[][] and it should work.
If it doesn't then use string[]* world (an array of array of strings is actually an array of pointers to an array of string)
I hope this helps, my C++ is becoming increasingly rusty.