ftp.nice.ch/peanuts/GeneralData/Usenet/news/1991/CSNProg-91.tar.gz#/comp-sys-next-programmer/1991/Dec/Problem-unarchiving-Storage-class

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Date: Sun 11-Dec-1991 18:43:25 
From: pmarcos@netcom.COM (Paul Marcos)
Subject: Problem unarchiving Storage class


Hi everyone,

I'm having trouble archiving a Storage object.  I have simplified it 
down to a simple app that has two fields, inField & outField.  I create
a storage object to store a single 10-character item using:

id myStorage;
myStorage = [[Storage alloc] initCount: 1 elementSize: 10 description: "*"];

I can then type something into inField which is type char *, and add it
to my storage objectusing:

[myStorage replace: inField at: 1]; (I don't have my printout in front
                                     of me so syntax may be wrong)

Anyway, it works and I can get the contents of the item using:

[outField setStringValue: [myStorage elementAt: 1]];

And everything works fine.  So now I try to write it off to a typed stream

NXTypedStream *myStream;
myStream = NXOpenTypedStreamForFile( myFile, NX_WRITEONLY );
NXWriteRootObject( myStream, myStorage );
NXCloseTypedStream( myStream );

I get the file written out and it looks OK to me.  When I try to unarchive
the object I use:

id newStorage;
myStream = NXOpenTypedStreamForFile( myFile, NX_READONLY );
newStorage = NXReadObject( myStream );
NXCloseTypedStream( myStream );

I would expect the same code that read the item out of myStorage could 
read the item out of newStorage but all I get is two characters that are
garbage.  If I query the object for it's count, elementSize and description
they are all OK.  

So what am I doing wrong.  I'd like to keep using the Storage object since 
it's so simple.  Any help?  Thanks.

Paul Marcos




Date: Sun 12-Dec-1991 17:00:28 
From: bedney@monolith.lanl.gov (William J. Edney)
Subject: Re: Problem unarchiving Storage class

In article <1991Dec11.184325.8063pmarcos@netcom.COM> pmarcos@netcom.COM  
(Paul Marcos) writes:
> 
> Hi everyone,
> 
> I'm having trouble archiving a Storage object.  I have simplified it 
> down to a simple app that has two fields, inField & outField.  I create
> a storage object to store a single 10-character item using:
> 
> id myStorage;
> myStorage = [[Storage alloc] initCount: 1 elementSize: 10 description:  
"*"];
> 
> I can then type something into inField which is type char *, and add it
> to my storage objectusing:
> 
> [myStorage replace: inField at: 1]; (I don't have my printout in front
>                                      of me so syntax may be wrong)
> 
> Anyway, it works and I can get the contents of the item using:
> 
> [outField setStringValue: [myStorage elementAt: 1]];
> 
> And everything works fine.  So now I try to write it off to a typed  
stream
> using:
> 
> NXTypedStream *myStream;
> myStream = NXOpenTypedStreamForFile( myFile, NX_WRITEONLY );
> NXWriteRootObject( myStream, myStorage );
> NXCloseTypedStream( myStream );
> 
> I get the file written out and it looks OK to me.  When I try to  
unarchive
> the object I use:
> 
> id newStorage;
> myStream = NXOpenTypedStreamForFile( myFile, NX_READONLY );
> newStorage = NXReadObject( myStream );
> NXCloseTypedStream( myStream );
> 
> I would expect the same code that read the item out of myStorage could 
> read the item out of newStorage but all I get is two characters that are
> garbage.  If I query the object for it's count, elementSize and  
description
> they are all OK.  
> 
> So what am I doing wrong.  I'd like to keep using the Storage object  
since 
> it's so simple.  Any help?  Thanks.
> 
> Paul Marcos

Paul -
Welcome to the world of NeXTstep, where even though most of the time the  
appkit is great, other times it falls flat on its face. The archiving  
methods in Storage are brain-damaged and will not write data contained  
therein properly. You must do this manually. I faced this problem and,  
with a lot of help from Dick Phillips (thanks, Dick!), won! Now, observe  
closely (I'm actually archiving a struct here, which makes things a bit  
more complex):
Here's some declarations I make in my .h:

typedef struct _ListElement {
	char		*descriptor;
	char		*description;
	} ListElement;

#define	LISTTYPE	ListElement *

Here's how I initialize the object in my init:
listList = [[Storage alloc] initCount:0
		elementSize:sizeof(LISTTYPE)
		description:@encode(LISTTYPE)];

Here's how I write it:
- write:(NXTypedStream *)stream
{
	int	i,theCount;
	LISTTYPE	*theElement;

	[super write:stream];
	
	theCount = [listList count];
	NXWriteType(stream,"i",&theCount);

	for (i=0;i<theCount;i++)
	{
		theElement = (LISTTYPE *)[listList elementAt:i];
		NXWriteType(stream,"*",&((*theElement)->descriptor));
		NXWriteType(stream,"*",&((*theElement)->description));
	}

	return self;
}

Here's how I read it:
- read:(NXTypedStream *)stream
{
	int			i,numElements;
	char			*theDescriptor,*theDescription;

	[super read:stream];

	NXReadType(stream,"i",&numElements);

	listList = [[Storage alloc] initCount:0
				elementSize:sizeof(LISTTYPE)
				description:@encode(LISTTYPE)];

	for (i=0; i<numElements; i++ )
	{
		NXReadType(stream,"*",&theDescriptor);
		NXReadType(stream,"*",&theDescription);

		[self addListElement:theDescriptor :theDescription];
	}

	return self;
}

Hope this helps!!
Good luck!!

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