Modifying 3 dimensional array in function in C

Question

I have a 3D array declared in main() function: char currentPositions[5][6][2]; And i want to modify this array using another function: SetDefaultPositions(currentPositions); This function looks something like this:

void setDefaultPositions(char positions[5][6][2]){
    char defaultPositions[5][6][2] = {
        {"()", "()", "..", "..", "..", ".."},
        {"/\\", "/\\", "/\\", "/\\", "/\\", "/\\"},
        {"..", "..", "..", "..", "..", ".."},
        {"/\\", "/\\", "/\\", "/\\", "/\\", "/\\"},
        {"..", "..", "..", "..", "..", ".."}
    };
    positions = defaultPositions;
}

I tried using pointers but it keeps telling me things like this: expected 'char (**)[2]' but argument is of type 'char (*)[6][2]' warning: passing argument 1 of 'setDefaultPositions' from incompatible pointer type [-Wincompatible-pointer-types] Or no errors, but printing currentPositions showed that it was empty. I understand nothing, I also tried some solutions from web but I can't find someone with similar problem. It's school project and I am not allowed to use global variables.

Answer 1

You can't pass an array to a C function. It decays to a pointer.
You can do it like this:

#include <stdio.h>
#include <stdlib.h>

void setDefaultPositions(size_t size, char positions[5][6][2]){
    char defaultPositions[5][6][2] = {
        {"()", "()", "..", "..", "..", ".."},
        {"/\\", "/\\", "/\\", "/\\", "/\\", "/\\"},
        {"..", "..", "..", "..", "..", ".."},
        {"/\\", "/\\", "/\\", "/\\", "/\\", "/\\"},
        {"..", "..", "..", "..", "..", ".."}
    };
    memcpy(positions, defaultPositions, size);
}

int main(void)
{
    char arr[5][6][2];
    setDefaultPositions(sizeof arr, arr);
    for(int j = 0; j < 5; j++) {
        for(int i = 0; i < 6; i++) {
            printf("%.2s ", arr[j][i]);
        }
        printf("\n");
    }
    return 0;
}

Program output:

() () .. .. .. .. 
/\ /\ /\ /\ /\ /\ 
.. .. .. .. .. .. 
/\ /\ /\ /\ /\ /\ 
.. .. .. .. .. .. 

Bear in mind that the array elements are not strings – they have no terminator.