test3.c

#include <stdio.h>  
#include <stdlib.h>  
#include <fcntl.h>  
int lcd;

void test() {
  int k, i, sum;
  char s[3];
  memset(s, '2', sizeof(s));
  printf("test begin!\n");

  k = lseek(lcd, 4, SEEK_CUR);
  printf("lseek = %d\n", k);

  k = write(lcd, s, sizeof(s));
  printf("written = %d\n", k);

  k = lseek(lcd, 0, SEEK_END);
  printf("lseek = %d\n", k);

  k = lseek(lcd, -4, SEEK_END);
  printf("lseek = %d\n", k);
}

void initial(char i) {
  char s[10];
  memset(s, i, sizeof(s));
  write(lcd, s, sizeof(s));
  char c[20] = "";
  int k = lseek(lcd, 0, SEEK_SET);
  printf("lseek = %d\n", k);
}

int main(int argc, char **argv) {
  lcd = open("/dev/onebyte", O_RDWR);
  if (lcd == -1) {
    printf("unable to open device");
    exit(EXIT_FAILURE);
  }     initial('1');
  test();
  close(lcd);
  return 0;
}