从源文件中读出最后10KB内容到目的文件中

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

#define BUFFSIZE 1024
#define offset 10240

int main(int argc,char *argv[])
{
 char buf[BUFFSIZE];
 int src_file,dest_file,real_read_num;
 
 /* check the input */
 if(argc != 3)
 {
  fprintf(stderr,"Usage:./copy_file source_file_name dest_file_name.\n");
  exit(1);
 }
 
 /* open source file for read only*/
 src_file = open(argv[1],O_RDONLY);
 /* open destination file only for write,if the file is not exist,then creat and access mode is 0644 */
 dest_file = open(argv[2],O_WRONLY | O_CREAT,S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
 
 /* check open operation is success or not */
 if(src_file < 0 || dest_file < 0)
 {
  perror("open");
  exit(2);
 }

 /* reposition the file pointer to the specified location */
 lseek(src_file,-offset,SEEK_END);

 /* read source file's content and write it to destination file */
 while((real_read_num = read(src_file,buf,BUFFSIZE)) > 0)
 {
  if(write(dest_file,buf,real_read_num) < 0)
  {
   perror("write");
   exit(3);
  }
 }

 close(src_file);
 close(dest_file);
 return 0;
}