deep copying

[bob@blah.com]

hi,

I have been tasked with transferring a rather complex, deeply nested
structure across dll's / memory spaces and effectively I need to deep
copy the structure in question. Its a C struct and it contains
pointers. I would have liked to think I could copy construct it, but I
can't. I need to follow the pointers.

Does anybody know if there's a quick and easy way to achieve this (as
opposed to manually following the pointers and fields which go 8-15
levels deep). I'm trying to see if boost can help me out but so far I
haven't seen anything.

Does anybody know whats the best approach to take here? I'm open to
all options.... i.e. anything but manually follow those 15
levels!! :) :) I'm fairly sure I'm reinventing the wheel, hence the
question. The struct in question is a C struct, used in a c++ app
(visual studio/borland, if its important).

thanks for any info.

Graham

[Victor Bazarov]

Re: deep copying

bob@blah.com wrote:

I have been tasked with transferring a rather complex, deeply nested
structure across dll's / memory spaces and effectively I need to deep
copy the structure in question. Its a C struct and it contains
pointers. I would have liked to think I could copy construct it, but I
can't. I need to follow the pointers.
>
Does anybody know if there's a quick and easy way to achieve this (as
opposed to manually following the pointers and fields which go 8-15
levels deep). I'm trying to see if boost can help me out but so far I
haven't seen anything.
>
Does anybody know whats the best approach to take here? I'm open to
all options.... i.e. anything but manually follow those 15
levels!! :) :) I'm fairly sure I'm reinventing the wheel, hence the
question. The struct in question is a C struct, used in a c++ app
(visual studio/borland, if its important).

Something in line with

// for members that are built-in or structs
template<class Tclass deepcopy {
static void go(T& dest, T const& src) {
dest = src;
}
};

// for the members that are pointers
template<class Tclass deepcopy<T*{
static void go(T* dest, T const* src) {
return deepcopy<T>::go (*dest, *src);
}
};

// and you only need to implement a real 'deepcopy' for your
// top-level struct (everything else should just fall into place)
void deepcopy(mystru ct& dest, mystruct const& src) {
deepcopy(dest.m ember_one, src.member_one) ;
...
}

V
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[Mark P]

Re: deep copying

Victor Bazarov wrote:

bob@blah.com wrote:

>I have been tasked with transferring a rather complex, deeply nested
>structure across dll's / memory spaces and effectively I need to deep
>copy the structure in question. Its a C struct and it contains
>pointers. I would have liked to think I could copy construct it, but I
>can't. I need to follow the pointers.
>>
>Does anybody know if there's a quick and easy way to achieve this (as
>opposed to manually following the pointers and fields which go 8-15
>levels deep). I'm trying to see if boost can help me out but so far I
>haven't seen anything.
>>
>Does anybody know whats the best approach to take here? I'm open to
>all options.... i.e. anything but manually follow those 15
>levels!! :) :) I'm fairly sure I'm reinventing the wheel, hence the
>question. The struct in question is a C struct, used in a c++ app
>(visual studio/borland, if its important).

>
Something in line with
>
// for members that are built-in or structs
template<class Tclass deepcopy {
static void go(T& dest, T const& src) {
dest = src;
}
};
>
// for the members that are pointers
template<class Tclass deepcopy<T*{
static void go(T* dest, T const* src) {
return deepcopy<T>::go (*dest, *src);
}
};
>
// and you only need to implement a real 'deepcopy' for your
// top-level struct (everything else should just fall into place)
void deepcopy(mystru ct& dest, mystruct const& src) {
deepcopy(dest.m ember_one, src.member_one) ;
...
}
>
V

I don't understand this. Should the last line of code that you wrote
(the implementation of the deepcopy function) be:

deepcopy<member _type>::go( dest.member_one , src.member_one) ;

If so, I don't see how this can work in the following situation:

struct A
{
B b;
};

struct B
{
C* c;
};

struct C
{
int x;
};


According to your prescription, we implement deepcopy for the top-level
struct A as:

void deepcopy( A& dest, const A& src)
{
deepcopy<B>::go ( dest.b, src.b);
}

The internal call to deepcopy leads to dest.b = src.b. But if B does
not have a deep copy assignment operator defined, we end up with a
shallow copy of C* c.

What am I missing here?

-Mark

[Victor Bazarov]

Re: deep copying

Mark P wrote:

Victor Bazarov wrote:

>bob@blah.com wrote:

>>I have been tasked with transferring a rather complex, deeply nested
>>structure across dll's / memory spaces and effectively I need to
>>deep copy the structure in question. Its a C struct and it contains
>>pointers. I would have liked to think I could copy construct it,
>>but I can't. I need to follow the pointers.
>>>
>>Does anybody know if there's a quick and easy way to achieve this
>>(as opposed to manually following the pointers and fields which go
>>8-15 levels deep). I'm trying to see if boost can help me out but
>>so far I haven't seen anything.
>>>
>>Does anybody know whats the best approach to take here? I'm open to
>>all options.... i.e. anything but manually follow those 15
>>levels!! :) :) I'm fairly sure I'm reinventing the wheel, hence the
>>question. The struct in question is a C struct, used in a c++ app
>>(visual studio/borland, if its important).

>>
>Something in line with
>>
> // for members that are built-in or structs
> template<class Tclass deepcopy {
> static void go(T& dest, T const& src) {
> dest = src;
> }
> };
>>
> // for the members that are pointers
> template<class Tclass deepcopy<T*{
> static void go(T* dest, T const* src) {
> return deepcopy<T>::go (*dest, *src);
> }
> };
>>
> // and you only need to implement a real 'deepcopy' for your
> // top-level struct (everything else should just fall into place)
> void deepcopy(mystru ct& dest, mystruct const& src) {
> deepcopy(dest.m ember_one, src.member_one) ;
> ...
> }
>>
>V

>
I don't understand this.

You actually understood much more than you give yourself credit for.

Should the last line of code that you wrote
(the implementation of the deepcopy function) be:
>
deepcopy<member _type>::go( dest.member_one , src.member_one) ;

Right.

I ought to define one more function:

template<class Tvoid deepcopy(T &t, T const& tt) {
return deepcopy<T>::go (t, tt);
}

>
If so, I don't see how this can work in the following situation:
>
struct A
{
B b;
};
>
struct B
{
C* c;
};
>
struct C
{
int x;
};
>
>
According to your prescription, we implement deepcopy for the
top-level struct A as:
>
void deepcopy( A& dest, const A& src)
{
deepcopy<B>::go ( dest.b, src.b);
}
>
The internal call to deepcopy leads to dest.b = src.b. But if B does
not have a deep copy assignment operator defined, we end up with a
shallow copy of C* c.
>
What am I missing here?

Not too much. You're on the right track, AFAICT.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask