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

  • From: "qubit" <lauraeaves@xxxxxxxxx>
  • To: <programmingblind@xxxxxxxxxxxxx>
  • Date: Wed, 30 Jun 2010 17:30:00 -0500

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
>> hierarchy.__________
>> View the list's information and change your settings at
>> //www.freelists.org/list/programmingblind
>>
>> __________
>> View the list's information and change your settings at
>> //www.freelists.org/list/programmingblind
>>
>
> __________
> View the list's information and change your settings at
> //www.freelists.org/list/programmingblind
>
> __________
> View the list's information and change your settings at
> //www.freelists.org/list/programmingblind
>

__________
View the list's information and change your settings at
//www.freelists.org/list/programmingblind

__________
View the list's information and change your settings at 
//www.freelists.org/list/programmingblind

Other related posts:

  1. Home
  2. programmingblind
  3. Archive
  4. 06-2010