這個書里的程序好象錯了？

#include "unp.h"
size_t          /* Read "n" bytes from a descriptor */
readn(int fd,void *vptr,size_t n)
{
     ssize_t   nleft,nread;
     char      *ptr;
     ptr=vptr;
     nleft=n;
     while(nleft >0) {
             if((nread=read(fd,ptr,nleft))<0) {
                     if(errno==EINTR)
                               nread=0 ;   /* and call read() again */
                     else
                               return(-1);
             }else if(nread ==0 )
                     break;             /*EOF*/
            nleft -= nread;
            ptr += nread ;
     }
     return(n-nleft);        /* return >= 0 */
}