CODEWITHSUNDEEP
cmultidimensional-array
tomashauser
tomashauser

Reputation: 571

Casting double int pointer to a regular 2D array

I have this global enum and a 3D array:

enum place { SCISSORS, DRILL, BENDING_MACHINE, WELDER, PAINT_SHOP, SCREWDRIVER, MILLING_CUTTER };

const int placeRecipeIndexes[_PLACE_COUNT][_PHASE_COUNT][TOOLS_REPEAT_COUNT] = {
        [SCISSORS] = {{0, EMPTY}, {1, EMPTY}, {EMPTY, EMPTY}},
        [DRILL] = {{1, 4}, {0, 3}, {1, 3}},
        [BENDING_MACHINE] = {{2, EMPTY}, {EMPTY, EMPTY}, {EMPTY, EMPTY}},
        [WELDER] = {{3, EMPTY}, {EMPTY, EMPTY}, {EMPTY, EMPTY}},
        [PAINT_SHOP] = {{5, EMPTY}, {4, EMPTY}, {5, EMPTY}},
        [SCREWDRIVER] = {{EMPTY, EMPTY}, {5, EMPTY}, {2, EMPTY}},
        [MILLING_CUTTER] = {{EMPTY, EMPTY}, {2, EMPTY}, {0, 4}}
};

and I need a pointer (or possibly a copy) which points to a particular 2D sub-array of placeRecipeIndexes which means that by pointing to placeRecipeIndexes[0], I would have a 2D array looking like this:

{{0, EMPTY}, {1, EMPTY}, {EMPTY, EMPTY}}.

At first, I tried it without a pointer: const int indexes[_PHASE_COUNT][TOOLS_REPEAT_COUNT] = toolsIndexes[idx]; but it gave me:

Array initializer must be an initializer list.

so I tried to do it like this:

const int **indexes = (const int **) toolsIndexes[idx];

but I can't access the indexes array positions because they're presumably empty - I'm getting SIGSEV.

I thought that this should definitely work. Am I missing something important here?

MRE:

#include <stdio.h>

#define EMPTY -1

enum place { SCISSORS, DRILL, BENDING_MACHINE, WELDER, PAINT_SHOP, SCREWDRIVER, MILLING_CUTTER };

const int placeRecipeIndexes[7][3][2] = {
        [SCISSORS] = {{0, EMPTY}, {1, EMPTY}, {EMPTY, EMPTY}},
        [DRILL] = {{1, 4}, {0, 3}, {1, 3}},
        [BENDING_MACHINE] = {{2, EMPTY}, {EMPTY, EMPTY}, {EMPTY, EMPTY}},
        [WELDER] = {{3, EMPTY}, {EMPTY, EMPTY}, {EMPTY, EMPTY}},
        [PAINT_SHOP] = {{5, EMPTY}, {4, EMPTY}, {5, EMPTY}},
        [SCREWDRIVER] = {{EMPTY, EMPTY}, {5, EMPTY}, {2, EMPTY}},
        [MILLING_CUTTER] = {{EMPTY, EMPTY}, {2, EMPTY}, {0, 4}}
};

int main() {
    const int **indexes = (const int **) placeRecipeIndexes[0];

    printf("{");
    for (int i = 0; i < 3; i++) {
        printf("{%d, ", indexes[i][0]);
        if (i != 2) {
            printf("%d}, ", indexes[i][1]);
        }
        else {
            printf("%d}", indexes[i][1]);
        }
    }
    printf("}\n");

    // The output should be: {{0, -1}, {1, -1}, {-1, -1}}
    return 0;
}

Upvotes: 2

Views: 46

Answers (1)

dxiv
dxiv

Reputation: 17648

Replace:

    const int **indexes = (const int **) placeRecipeIndexes[0];

with:

    const int (*indexes)[2] = placeRecipeIndexes[0];     // C

or:

    const int (&indexes)[3][2] = placeRecipeIndexes[0];  // C++

For verification, the following check out (in C++):

static_assert(&indexes[0][0] == &placeRecipeIndexes[0][0][0]);
static_assert(&indexes[2][1] == &placeRecipeIndexes[0][2][1]);

Upvotes: 1

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