Re: serialization, size errors... or something else.

  • From: "qubit" <lauraeaves@xxxxxxxxx>
  • To: <programmingblind@xxxxxxxxxxxxx>
  • Date: Wed, 30 Jun 2010 17:57:19 -0500

oh, ok, the virtual doesn't apply then -- you've been at this a long time 
now so should know a lot of that stuff already.
If however you are using fwrite to serialize a type parameter, what's to 
prevent that parameter from being a class type that might not work well with 
that kind of arrangement? Of course if you did pass it a class type, then 
fwrite would complain about a type mismatch.
well, I'm sure you'll figure it out.  If you have any other thoughts or 
questions, feel free to fire off an email.
as always, happy hacking.
--le

--le





----- Original Message ----- 
From: "Tyler Littlefield" <tyler@xxxxxxxxxxxxx>
To: <programmingblind@xxxxxxxxxxxxx>
Sent: Wednesday, June 30, 2010 5:40 PM
Subject: Re: serialization, size errors... or something else.


I'm not passing pointers to classes though. the serialization function just 
does like s << level; etc. It only serializes fields in the class.
Thanks,
Tyler Littlefield
http://tds-solutions.net
Twitter: sorressean

On Jun 30, 2010, at 4:30 PM, qubit wrote:

> what I'm trying to prevent with all these questions is the inadvertent
> pointer shift that happens when you say B *bp = d; where d is of a type
> derived from b, and there is multiple inheritance.
> It's a nasty gotcha that may have been eliminated in more recent 
> definitions
> of C++, but I don't know so am warning you.
>
> Anyway, I also wanted to be sure you don't forget that things like virtual
> pointers are embedded somewhere in the body of a class.  These take up
> space, and if you write sizeof(T) bytes then you will include the virtual
> pointers, but if you are expecting just to get visible data then the
> calculation will be off.
>
> Now if you don't do virtual functions, you'll have to think in another
> direction.
> Any closer?
>
> ----- Original Message ----- 
> From: "Tyler Littlefield" <tyler@xxxxxxxxxxxxx>
> To: <programmingblind@xxxxxxxxxxxxx>
> Sent: Wednesday, June 30, 2010 5:16 PM
> Subject: Re: serialization, size errors... or something else.
>
>
> What do you mean I'm passing it around as different types? Fwrite takes 
> the
> size of the block your writing, the number of blocks, and the file to 
> write
> to, as well as the block. so you supply 1 for the count, sizelf(T), and 
> the
> address of t. T is just the templated type. It looks something like:
> template <class T>
> void Write(const &T data)
>
> Thanks,
> Tyler Littlefield
> http://tds-solutions.net
> Twitter: sorressean
>
> On Jun 30, 2010, at 4:13 PM, qubit wrote:
>
>> Ok, the plot thickens -- did you cast the address of the pointer to a
>> char*
>> to pass to fwrite? Maybe a dumb question but I'm just feeling this out.
>> You have p being of some type T* and you say
>>   fwrite(fp, (char*)p, sizeof(T));
>> Is this done in a template function where you don't know the final type 
>> of
>> T?
>> What is T anyway?
>> I'm just hoping some funny pointer arithmetic is not getting done on p
>> because you are passing it around as different types.
>> Any progress?
>> --le
>>
>>
>> ----- Original Message ----- 
>> From: "Tyler Littlefield" <tyler@xxxxxxxxxxxxx>
>> To: <programmingblind@xxxxxxxxxxxxx>
>> Sent: Wednesday, June 30, 2010 4:55 PM
>> Subject: Re: serialization, size errors... or something else.
>>
>>
>> Basically what I did was used a templated function to write, then I write
>> the arg with fwrite, and use sizeof(T) to get the size. Reading does the
>> same thing, I also overloaded operators << and >> to read and write.
>> Thanks,
>> Tyler Littlefield
>> http://tds-solutions.net
>> Twitter: sorressean
>>
>> On Jun 30, 2010, at 3:53 PM, qubit wrote:
>>
>>> without knowing a little about your serialization strategy, it's hard to
>>> diagnose what might be wrong.
>>> Do you do something similar to Boost, or do you have some other
>>> algorithm?
>>> --le
>>>
>>> ----- Original Message ----- 
>>> From: "Tyler Littlefield" <tyler@xxxxxxxxxxxxx>
>>> To: <programmingblind@xxxxxxxxxxxxx>
>>> Sent: Wednesday, June 30, 2010 4:02 PM
>>> Subject: Re: serialization, size errors... or something else.
>>>
>>>
>>> I do know I'm reading to much because I get a size excception. I'm not
>>> sure
>>> how to cut this down because the serialization works through an
>>> inheritance
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