#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; }