Thread overview
Issue De-referencing a Pointer to a Struct in an Array
Jul 14, 2023
Pen Hall
Jul 14, 2023
Pen Hall
Jul 14, 2023
Pen Hall
July 14, 2023

Hello!
In my program, I have defined a struct called Tile in the global scope. In my main() function I create a 3d array of Tiles called board. I then have a function called loopBoard() that loops through certain parts of board. I then create a reference to the Tile struct at the current position of board. This all works until I try to de-reference that pointer. The result compiles, but I get the exit code -1073741819 whenever I run it. Below is the function in question. Do any of you have literally any clue about where I'm screwing up?

void loopBoard(Tile[8][8][8]* board, void function(int, int, int, Tile*) func){
	for(int number = 7; number >= 0; number--){
		writeln(number);
		for(int symbol = 7 - number; symbol < 8; symbol++) {
			writeln("  " ~ to!string(symbol));
			//((x % y) + y) % y to make modulo work as expected
			int letter = (((symbol - 7) % 7) + 7) % 7;
			if(letter == 0 && symbol != 0)
				letter += 7;

			int[2] lArr;
			lArr[0] = letter;
			lArr[1] = (letter != 7) ? letter + 1 : -1;
			writeln("    [" ~ to!string(lArr[0]) ~", " ~ to!string(lArr[1]) ~ "]");

			for(int i = 0; i < lArr.length; i++){
				
				Tile * tile = (board[number][symbol][i]).ptr;

				//program runs well until I reach this point, then it crashes
				writeln("\t", *tile);
				func(number,symbol,lArr[i], tile);
			}

			
		}
	}
}
July 14, 2023

On Friday, 14 July 2023 at 16:57:33 UTC, Pen Hall wrote:

>

Hello!
In my program, I have defined a struct called Tile in the global scope. In my main() function I create a 3d array of Tiles called board. I then have a function called loopBoard() that loops through certain parts of board. I then create a reference to the Tile struct at the current position of board. This all works until I try to de-reference that pointer. The result compiles, but I get the exit code -1073741819 whenever I run it. Below is the function in question. Do any of you have literally any clue about where I'm screwing up?

[...]

I realized a slight issue with this code is that board[number][symbol][i] refers to an array... somehow. I genuinely have no idea as to why this is.

July 14, 2023

On Friday, 14 July 2023 at 17:14:01 UTC, Pen Hall wrote:

>

On Friday, 14 July 2023 at 16:57:33 UTC, Pen Hall wrote:

>

Hello!
In my program, I have defined a struct called Tile in the global scope. In my main() function I create a 3d array of Tiles called board. I then have a function called loopBoard() that loops through certain parts of board. I then create a reference to the Tile struct at the current position of board. This all works until I try to de-reference that pointer. The result compiles, but I get the exit code -1073741819 whenever I run it. Below is the function in question. Do any of you have literally any clue about where I'm screwing up?

[...]

I realized a slight issue with this code is that board[number][symbol][i] refers to an array... somehow. I genuinely have no idea as to why this is.

I think i figured out my issue...
The issue was that 'board' is a pointer, and all of the ways I tried to de-reference it, failed. I just tried the form (*board)[number][symbol][letter] which worked to de-reference it. &(*board)[number][symbol][letter], of course, works to get a pointer to that spot in memory.

July 14, 2023

On 7/14/23 1:23 PM, Pen Hall wrote:

>

I think i figured out my issue...
The issue was that 'board' is a pointer, and all of the ways I tried to de-reference it, failed. I just tried the form (*board)[number][symbol][letter] which worked to de-reference it. &(*board)[number][symbol][letter], of course, works to get a pointer to that spot in memory.

A nice abstraction available in D is a nested function.

e.g.:

ref boardRef => *board;
// or with traditional syntax:
ref Tile[8][8][8] boardRef() { return *board; }

This should allow you to use boardRef[number][symbol][i]

-Steve