#include<stdio.h>#include<unistd.h>#include<fcntl.h>#include<stdlib.h>int main(void){    int fd;    char buf[10];    int n;    fd=open("test.txt",O_RDWR);    if(fd==-1)    {        perror("fail to open");        exit(1);    }    else        printf("open OK!\n");    printf("Reading...\n");    n=read(fd,buf,10);    if(n==-1)    {        perror("fail to read");        exit(1);    }    buf[n]='\0';    printf(buf);    close(fd);    return 0;}