six.c

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

int main(void) {
  
  int count = 9;
  char *buf = calloc(count + 1, 1);
  fread(buf, count, 1, stdin);
  
  
  char a[7]; // 6 chars + \0
  strncpy(a, buf, sizeof(a) - 1);
  a[sizeof(a) - 1] = '\0'; // strncpy doesn't add \0
  printf("a: '%s'\n", a);

  
  char b[7] = {0}; // explicit zeroing
  strncat(b, buf, sizeof(b) - 1);
  printf("b: '%s'\n", b);

  return 0;
}