How do I pass a reference to a two-dimensional array to a function?

Question

I am trying to pass a reference to a two-dimensional array to a function in C++. I know the size of both dimensions at compile time. Here is what I have right now: ``` const int board_width = 80; const int board_height = 80; void do_something(int[board_width][board_height]& array); //function prototype ``` But this doesn't work. I get this error from g++: ``` error: expected ‘,’ or ‘...’ before ‘*’ token ``` What does this error mean, and how can I fix it?

Accepted Answer

If you know the size at compile time, this will do it:

```
//function prototype
void do_something(int (&array)[board_width][board_height]);
```

Doing it with

```
void do_something(int array[board_width][board_height]);
```

Will actually pass a pointer to the first sub-array of the two dimensional array ("board_width" is completely ignored, as with the degenerate case of having only one dimension when you have `int array[]` accepting a pointer), which is probably not what you want (because you explicitly asked for a reference). Thus, doing it with the reference, using sizeof on the parameter `sizeof array` will yield `sizeof(int[board_width][board_height])` (as if you would do it on the argument itself) while doing it with the second method (declaring the parameter as array, thus making the compiler transform it to a pointer) will yield `sizeof(int(*)[board_height])`, thus merely the sizeof of a pointer.

How do I pass a reference to a two-dimensional array to a function?

Solution

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