#include<stdio.h>

#define SZ 3

typedef struct {
    int x[SZ];
} *pthrowaway;

int main(void)
{
    int A[SZ]={1,2,3};
    int B[4][SZ]={0};
    int row_select=2;

    int i, j;

    for(i = 0; i < 4; i++) {
        for(j = 0; j < SZ; j++) {
            printf("%d ", B[i][j]);
        }
        printf("\n");
    }

    *(pthrowaway)&B[row_select] = *(pthrowaway)&A;

     for(i = 0; i < 4; i++) {
        for(j = 0; j < SZ; j++) {
            printf("%d ", B[i][j]);
        }
        printf("\n");
    }

    return 0;
}