How to convert struct to char array in C

#include <stdio.h>

struct x
{
   int x;
} __attribute__((packed));


int main()
{
   struct x a;
   a.x=127;
   char *b = (char *)&a;
   int i;
   for (i=0; i<4; i++)
      printf("%02x ", b[i]);
   printf("n");
   for (i=0; i<4; i++)
      printf("%d ", b[i]);
   printf("n");
   return 0;
}

printf("%02hhx", b[i]);

for (i=0; i<4; i++)
   printf("%02x ", (unsigned char)b[i]);

unsigned char *b = (unsigned char *)&a;

for (i=0; i<4; i++) {
//...
}

for (i=0; i<sizeof(x); i++) {
//...
}