#include <stdlib.h>
#include <stdio.h>
#define ARR_LEN 6
int main() {
char buff[ARR_LEN];
int i;
  for(i=0; i<ARR_LEN; i++){
  buff[i] = i + '0';
}
snprintf(buff, ARR_LEN, "012345");
puts(buff);
}

buffersnprintf.c: In function ‘main’:
buffersnprintf.c:10:32: warning: ‘snprintf’ output truncated before the last format character [-Wformat-truncation=]
 snprintf(buff, ARR_LEN, "012345");
                                ^
buffersnprintf.c:10:1: note: ‘snprintf’ output 7 bytes into a destination of size 6
 snprintf(buff, ARR_LEN, "012345");
 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~