C實現檔案拷貝

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <string.h>
#define BUFFER_SIZE 1024
int main(int argc,char** argv)
{
 int from_fd,to_fd;
 int bytes_read,bytes_write;
 char buffer[BUFFER_SIZE];
 char* ptr;
 if(argc != 3)
 {
  fprintf(stderr,"Usage: %s fromfile tofile\n\a",argv[0]);
  exit(1);
 }
 /*開啟源檔案*/
 if((from_fd = open(argv[1],O_RDONLY)) == -1)
 {
  fprintf(stderr,"Open %s Error: %s\n",argv[1],strerror(errno));
  exit(1);
 }
 /*建立目的檔案*/
 if((to_fd = open(argv[2],O_WRONLY|O_CREAT,S_IRUSR|S_IWUSR)) == -1)
 {
  fprintf(stderr,"Open %s Error: %s\n",argv[2],strerror(errno));
  exit(1);
 }
 /*以下代碼是一個經典的拷貝檔案的代碼*/
 while(bytes_read = read(from_fd,buffer,BUFFER_SIZE))
 {
  /*一個致命的錯誤發生了*/
  if((bytes_read == -1)&&(errno != EINTR)) break;
  else if(bytes_read > 0)
  {
   ptr = buffer;
   while(bytes_write = write(to_fd,ptr,bytes_read))
   {
    /*一個致命的錯誤發生了*/
    if((bytes_write == -1)&&(errno != EINTR)) break;
    /*寫完了所有讀的位元組*/
    else if(bytes_write == bytes_read) break;
    /*唯寫了一部分，繼續寫*/
    else if(bytes_write > 0)
    {
     ptr += bytes_write;
     bytes_read -= bytes_write;
    }
   }
   /*寫的時候發生致命錯誤*/
   if(bytes_write == -1) break;
  }
 }
 close(from_fd);
 close(to_fd);
 exit(0);
}