Linux平台下利用系统接口函数按照行读写文件

#include<stdio.h>
#include<fcntl.h>
#include<stdlib.h>
#include<string.h>
#define rwmode 2

//清屏命令函数
void clear()
{
char clscode[] = {0x1B, 0x5B, 0x48, 0x1B, 0x5B, 0x4A};
printf("%s",clscode);
}

//打开文件
int openFile()
{
int fd;
fd=open("/root/wcy/test1/test.txt",rwmode);
if(fd==-1){
printf("打开文件失败,文件路径不正确或者文件不存在！\n");
exit(0);
}else return fd;

}

//读取文件
void readFile(int fd,char buffer[],int len){

int n=read(fd,buffer,len);
buffer
='\0';
printf("文件的内容是:");
printf("%s",buffer);
printf("\n");
}

void lseekFile(int fd){

if(lseek(fd,0L,SEEK_END)==-1){
clear();
printf("定位读写文件失败！");
}
else{
char block[512]=" lseek file";
write(fd,block,strlen(block));
printf("定位读写文件成功！\n");
}

}

int main(){

int fd,n,select;
char buffer[1024*1024];
clear();
while(1){
printf("******************************\n") ;
printf("******   读写文件系统   ******\n");
printf("****  1 显示特定文件内容：****\n");
printf("****  2 定位读写文件内容：****\n");
printf("****  0 退出本系统       *****\n");
printf("******************************\n");
printf("请输入功能编号：");
scanf("%d",&select);
switch(select){

case 0:
clear();
close(fd);
exit(0);
case 1:
clear();
fd=openFile();
readFile(fd,buffer,sizeof(buffer)-1);
close(fd);
break;
case 2:
clear();
fd=openFile();
lseekFile(fd);
close(fd);
break;
default:
clear();
printf("你输入功能编号错误，请重新输入！\n");
}
}
exit(0);
}