c语言 函数返回二位数组 函数参数为二维数组

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

const int ROW = 3;
const int COL = 4;

typedef int (* mat_pointer)[COL];

mat_pointer init_mat(mat_pointer a)
{
    for (int i = 0; i < ROW; ++i)
        for (int j = 0; j < COL; ++j)
            a[i][j] = i + j;
    return a;
}

void print_mat(mat_pointer a)
{
    for (int i = 0; i < ROW; ++i)
        for (int j = 0; j < COL; ++j)
            printf("A[%d][%d]=%d%c", i, j, a[i][j], j == COL - 1 ? ‘\n‘ : ‘\t‘);
    printf("\n");
}

int (*build_mat(void))[COL]
{
    int (* arr_pointer)[COL] = (int (*)[COL]) malloc(ROW * COL * sizeof (int));
    for (int i = 0; i < ROW; ++i) {
        for (int j = 0; j < COL; ++j)
            arr_pointer[i][j] = i * 10 + j;
    }
    return arr_pointer;
}


int main(void)
{
    int arr[ROW][COL];

    mat_pointer arr2 = init_mat(arr);
    print_mat(arr2);

    int (*arr3)[COL] = build_mat();
    print_mat(arr3);

    return 0;
}