C实现文件拷贝

#include
#include
#include
#include
#include
#include
#include
#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);
 }
 /*打开源文件*/
 if((from_fd = open(argv[1],O_RDONLY)) == -1)
 {
  fprintf(stderr,"Open %s Error: %s\n",argv[1],strerror(errno));
  exit(1);
 }
 /*创建目的文件*/
 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);
 }
 /*以下代码是一个经典的拷贝文件的代码*/
 while(bytes_read = read(from_fd,buffer,BUFFER_SIZE))
 {
  /*一个致命的错误发生了*/
  if((bytes_read == -1)&&(errno != EINTR)) break;
  else if(bytes_read > 0)
  {
   ptr = buffer;
   while(bytes_write = write(to_fd,ptr,bytes_read))
   {
    /*一个致命的错误发生了*/
    if((bytes_write == -1)&&(errno != EINTR)) break;
    /*写完了所有读的字节*/
    else if(bytes_write == bytes_read) break;
    /*只写了一部分，继续写*/
    else if(bytes_write > 0)
    {
     ptr += bytes_write;
     bytes_read -= bytes_write;
    }
   }
   /*写的时候发生致命错误*/
   if(bytes_write == -1) break;
  }
 }
 close(from_fd);
 close(to_fd);
 exit(0);
}