Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!dptg!att!cbnewsl!dog
From: dog@cbnewsl.ATT.COM (edward.n.schiebel)
Newsgroups: comp.lang.c++
Subject: Re: Objectifying contents read in from disk
Message-ID: <1228@cbnewsl.ATT.COM>
Date: 24 Jul 89 19:14:19 GMT
References: <7316@athertn.Atherton.COM>
Distribution: usa
Organization: AT&T Bell Laboratories
Lines: 32

From article <7316@athertn.Atherton.COM>, by thanh@athertn.Atherton.COM (Thanh Diec):
.. stuff deleted
> Writer:
> 
>   // write out an array of 1024 objects 
> 
>   write(fd, &object_array[0], sizeof(class1) * 1024);
> 
>   
> Reader:
> 
>   read(fd, buf, sizeof(class1) * 1024);
>   
>   class1 *p1 = (class1 *)buf;		
> 
>   // buf is not ready to used as objects yet, must set runtime values
>   // such as _vptr's
> 
In our project, each class that may need to have instances read and write
themselves have read and write member functions which read and write
the member data.  On a read, the application creates an instance, then
calls the read function to fill it up.  There are a couple of small
problems:
	- this is not as fast as a block read like your example, but
	  then it doesn't need vptr fixing.
	- the object may have to output small headers ahead of some
	  member data as a type field
	  if the data is a pointer to a base class which may actually
	  pont to a derived class object.  If this is true, the object 
	  needs to know what type to create to call the proper reader.
	
  Ed Schiebel