Question

How to apply callback to dynamically allocated 2D array in C

Answer 1

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

// Dynamically allocated 2D array (array of pointers)

// A callback function applied to each element

/* -------------------- Allocation -------------------- */
int **allocate2D(int rows, int cols) {
    int **arr = malloc(rows * sizeof(int*));
    if (!arr) {
        perror("malloc failed");
        exit(1);
    }

    for (int r = 0; r < rows; r++) {
        arr[r] = malloc(cols * sizeof(int));
        if (!arr[r]) {
            perror("malloc failed");
            exit(1);
        }
    }

    return arr;
}

/* -------------------- Fill -------------------- */
void fill2D(int rows, int cols, int **arr, int startValue) {
    int v = startValue;
    for (int r = 0; r < rows; r++)
        for (int c = 0; c < cols; c++)
            arr[r][c] = v++;
}

/* -------------------- Print -------------------- */
void print2D(int rows, int cols, int **arr) {
    for (int r = 0; r < rows; r++) {
        for (int c = 0; c < cols; c++)
            printf("%d ", arr[r][c]);
        printf("\n");
    }
}

/* -------------------- Free -------------------- */
void free2D(int rows, int **arr) {
    for (int r = 0; r < rows; r++)
        free(arr[r]);
    free(arr);
}

/* -------------------- Callback Application -------------------- */
void apply2D(int rows, int cols, int **arr, void (*cb)(int*)) {
    for (int r = 0; r < rows; r++)
        for (int c = 0; c < cols; c++)
            cb(&arr[r][c]);
}

/* callback function */
void increment(int *x) {
    (*x)++;
}

/* -------------------- Main -------------------- */
int main() {
    int rows = 3, cols = 4;

    int **arr = allocate2D(rows, cols);

    fill2D(rows, cols, arr, 1);

    printf("Before callback:\n");
    print2D(rows, cols, arr);

    apply2D(rows, cols, arr, increment);

    printf("\nAfter callback:\n");
    print2D(rows, cols, arr);

    free2D(rows, arr);

    return 0;
}


 
/*
run:
 
Before callback:
1 2 3 4 
5 6 7 8 
9 10 11 12 

After callback:
2 3 4 5 
6 7 8 9 
10 11 12 13 
 
*/

 

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