What are the differences between an array of char pointers and a 2D array?

Question

What are the differences between an array of char pointers and a 2D array?

Answer 1

char* pasz[3] = {"abc", "def", "ghi"};
char asz[3][] = {"abc", "def", "ghi"};

The similarities and differences are basically the same as between these two:

char *psz = "jkl";
char sz[] = "jkl";

---

The first is originally read-only.

psz[0] = 'a'; // Illegal!!

The second, you can modify, since you allocate it with the [].

sz[0] = 'b';
// sz == "bkl"

---

The first, you can modify what it points to:

char mysz[] = "abc";
psz = mysz;

psz[0] = 'b';
// mysz == "bbc"

The second, you cannot:

sz = mysz; // Can't assign an array to an array!!

Answer 2

Array of arrays (aka multi-dimensional array) looks like (in memory):

a[0][0], a[0][1], a[0][n-1], a[1][0], a[1][1], ..., a[1][n-1], ..., a[m-1][n-1]

array of pointers looks like:

p[0], p[1], ..., p[m-1]

where each slot is a pointer and can point to whatever. If they all happen to point to arrays with n elements each, then p[i][j] and a[i][j] can be used similarly in expressions, but they're actually quite different objects.

Answer 3

char* my_string[];

represents an array of strings.

int my_grid_of_ints[][];
char my_block_of_text[][];

If color = byte[3] then you could represent your screen monitor

color my_pixel_buffer[][] = new color[768][1024];

is a 2D array. As you can see, a 2D array can represent anything, including an array of char pointers (such as multiple lines of strings).

Answer 4

You can access elements with the same syntax, but the guarantees about memory layout is much different. The 2d array is contiguous. The array of pointers is not.