[RESOLVED] vector copy using new

Hey.

I'm wanting to fill the vector below with newed copies of each element in vec_ref and I was wondering if there is a STL algorithm that I can take advantage of?

Code:

---

int main()
{
  std::vector<C> c_vec(10, C(1));
  const std::vector<C>& vec_ref = c_vec;

  std::vector<C*> new_c_vec;

  // ... copy vec_ref into new_c_vec using "new"

  return 0;
}

---

Cheers.

I find your question a little confusing. You say "newed copies" at the same time "of each element in vec_ref".

I think, a reasonable way of achieving this is to provide a clone() function for your class and then use std::transform.

Code:

---

class C {
  // ...
  virtual C* clone() { return new C(*this); }
}

---

Call to transform should look something like (not tested):

Code:

---

std::transform(c_vec.begin(), c_vec.end(),
              std::back_inserter(new_c_vec),
              mem_fun_ref(clone));

---

or, if you resize new_c_vec before like

Code:

---

std::transform(c_vec.begin(), c_vec.end(),
              new_c_vec.begin(),
              mem_fun_ref(clone));

---

Quote:

---

Originally Posted by treuss

I think, a reasonable way of achieving this is to provide a clone() function for your class and then use std::transform.

Code:

---

class C {
  // ...
  virtual C* clone() { return new C(*this); }
}

---

Call to transform should look something like (not tested):

Code:

---

std::transform(c_vec.begin(), c_vec.end(),
              std::back_inserter(new_c_vec),
              mem_fun_ref(clone));

---

or, if you resize new_c_vec before like

Code:

---

std::transform(c_vec.begin(), c_vec.end(),
              new_c_vec.begin(),
              mem_fun_ref(clone));

---

---

Nice idea! But in this case would it be better just to iterate through c_vec and push_back new Cs instead of creating the clone function? It won't be hard to change the classes that rely on this, but I'm just wondering which option you think is more professional.


Cheers. :thumb:

Please describe what you are going to do with the copied elements. Maybe it isn´t necessary to clone the vector by choosing a different approach than the one you´re implementing now.

Quote:

---

Originally Posted by GNiewerth

Please describe what you are going to do with the copied elements. Maybe it isn´t necessary to clone the vector by choosing a different approach than the one you´re implementing now.

---

Code:

---

    // Update screen elements.
    test_screen.Update(event_);
    // Draw(blit) elements to screen.
    test_screen.Draw(DE.Get_Screen());
    // Draw screen.
    DE.Draw_Screen();

---

In the real problem, they're going to be stored in a vector of base pointers (Base_XImage) which itself is stored in my Screen class. From there, each time Update or Draw gets called as above, each element in the vector of base pointers will have Update and Draw called polymorphically. The class hierarchy looks like this:

Code:

---

Base_XImage
  XImage
  XButton

---

Quote:

---

Originally Posted by Mybowlcut

Nice idea! But in this case would it be better just to iterate through c_vec and push_back new Cs instead of creating the clone function? It won't be hard to change the classes that rely on this, but I'm just wondering which option you think is more professional.

---

Basically I see three options:

• A clone function and using std::transform with mem_fun_ref
• A free function for cloning and using std::transform with the free function
• Not using std::transform but writing the loop yourself and creating the clone inline inside the loop

I'm not 100% sure, I understand your last post correctly, but if C is in fact a base class, I would definitely create the clone function. Note that the function should be virtual and all derived classes should of course return a pointer to a derived class. You will soon find that the clone function has a lot of uses. Think about creating a deep copy of a vector of base class pointers. Piece of cake ;-)

Quote:

---

Originally Posted by treuss

Basically I see three options:

• A clone function and using std::transform with mem_fun_ref
• A free function for cloning and using std::transform with the free function
• Not using std::transform but writing the loop yourself and creating the clone inline inside the loop

I'm not 100% sure, I understand your last post correctly, but if C is in fact a base class, I would definitely create the clone function. Note that the function should be virtual and all derived classes should of course return a pointer to a derived class.

---

Do you mean like this?

Code:

---

class C
{
public:
  C(int x_) : x(x_) {}
  virtual C* clone() { return new C(*this); }
  int x;
};

class D : public C
{
  D(int x) : C(x) {}
  virtual C* clone() { return new D(*this); }
};

---

Quote:

---

Originally Posted by treuss

You will soon find that the clone function has a lot of uses. Think about creating a deep copy of a vector of base class pointers. Piece of cake ;-)

---

It sounds good hey haha. Have you used this kind of function before?

D's override of clone() can return a D* instead. I believe this is the "covariant return type" thing.

What about a custom function object?

Code:

---

struct DrawFunc
{
  Screen S_;
  Event E_;
  DrawFunc( Screen& s, Event& e ) : S_( s ), E_( e )
  {
  }

  void operator()( C* pObj )
  {
      // do whatever you need to do with C, S_ and E_
  }
}

std::vector<C*> c_vec;

for_each( c_vec.begin(), c_vec.end(), DrawFunc( theScreen, theEvent ) );

---

I just wrote this lines down, I´m pretty sure they won´t compile, but i hope you got the idea.

Quote:

---

Originally Posted by Mybowlcut

Do you mean like this?

---

Better:

Code:

---

virtual D* clone() { return new D(*this); }

---

And of course you are lacking the virtual destructor in the example.

Quote:

---

Originally Posted by Mybowlcut

It sounds good hey haha. Have you used this kind of function before?

---

Yes and I think it is a common design pattern, I just can't recall where I first read about it (Scott Meyers' probably).

http://en.wikipedia.org/wiki/Prototype_pattern

Ok. I made the interface class Cloneable:

Code:

---

class Cloneable
{
public:
  virtual ~Cloneable() {}
  virtual Cloneable* Clone() = 0;
};

---

Then derived my base class from it:

Code:

---

class Base_XImage : public Drawable, public Updateable, public Cloneable
{
public:
  Base_XImage();
  Base_XImage(
    const std::string& file_name_,
    int position_x,
    int position_y,
    bool is_colour_key_,
    SDL_Colour colour_key_ = SDL_Wrappers::colour(0,0,0));
  Base_XImage(const Base_XImage& rhs);
  virtual ~Base_XImage();
 
  Base_XImage& operator=(const Base_XImage& rhs);

  const std::string& Get_File_Name() const;
  const SDL_Rect& Get_Position() const;
  bool Is_Colour_Key() const;
  const SDL_Colour& Get_Colour_Key() const;
 
  virtual void Load() = 0;
  virtual void Draw(SDL_Surface* screen) = 0;
  virtual void Update(const SDL_Event& event_) = 0;
  virtual Base_XImage* Clone() = 0;
protected:
  std::string file_name;
  SDL_Rect position;
  bool is_colour_key;
  SDL_Colour colour_key;
  SDL_Surface* surface;
};

---

Then I tried to use transform with it (buttons is a vector of XButtons which derive from Base_XImage:

Code:

---

std::transform(buttons.begin(), buttons.end(),
    std::back_inserter(elements), std::mem_fun_ref(&Base_XImage::Clone));

---

Code:

---

Error        1        error C2784: 'std::const_mem_fun1_ref_t<_Result,_Ty,_Arg> std::mem_fun_ref(_Result (__thiscall _Ty::* )(_Arg) const)' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        2        error C2784: 'std::const_mem_fun1_ref_t<_Result,_Ty,_Arg> std::mem_fun_ref(_Result (__thiscall _Ty::* )(_Arg) const)' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        3        error C2784: 'std::const_mem_fun1_ref_t<_Result,_Ty,_Arg> std::mem_fun_ref(_Result (__thiscall _Ty::* )(_Arg) const)' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        4        error C2914: 'std::mem_fun_ref' : cannot deduce template argument as function argument is ambiguous        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        5        error C2784: 'std::const_mem_fun_ref_t<_Result,_Ty> std::mem_fun_ref(_Result (__thiscall _Ty::* )(void) const)' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        6        error C2784: 'std::mem_fun1_ref_t<_Result,_Ty,_Arg> std::mem_fun_ref(_Result (__thiscall _Ty::* )(_Arg))' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        7        error C2784: 'std::mem_fun1_ref_t<_Result,_Ty,_Arg> std::mem_fun_ref(_Result (__thiscall _Ty::* )(_Arg))' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        8        error C2784: 'std::mem_fun1_ref_t<_Result,_Ty,_Arg> std::mem_fun_ref(_Result (__thiscall _Ty::* )(_Arg))' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        9        error C2914: 'std::mem_fun_ref' : cannot deduce template argument as function argument is ambiguous        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        10        error C2784: 'std::mem_fun_ref_t<_Result,_Ty> std::mem_fun_ref(_Result (__thiscall _Ty::* )(void))' : could not deduce template argument for 'overloaded function type' from 'overloaded function type'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68
Error        11        error C2780: '_OutIt std::transform(_InIt1,_InIt1,_InIt2,_OutIt,_Fn2)' : expects 5 arguments - 4 provided        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\screen.cpp        68

---

Anyone know what this is complaining about?

Beautiful error messages :rolleyes:

No idea, the call to transform looks correct. Try compiling the following (works with g++ and comeau), if that works try correcting your code accordingly. Or post a compilable sample of the problem ;)

Code:

---

#include <vector>
#include <algorithm>
#include <functional>

class Base
{
public:
  virtual Base * clone() const = 0;
  virtual ~Base() {}
};

class Derived : public Base
{
public:
  virtual Derived * clone() const { return new Derived(*this); }
  virtual ~Derived() {}
};

int main()
{
  std::vector<Derived> v1(3);

  std::vector<Base*> v2(3);
  std::transform(v1.begin(), v1.end(),
                v2.begin(),
                std::mem_fun_ref(&Base::clone));

  std::vector<Base*> v3;
  std::transform(v1.begin(), v1.end(),
                std::back_inserter(v3),
                std::mem_fun_ref(&Base::clone));
}

---

EDIT: Just noticed that your clone function is not const. Don't know if that matters but it should of course be.

Could it be that buttons is a vector of objects whilst elements is a vector of object pointers? Unfortunately I can't really post a working example as my code uses a third party library.

Quote:

---

Originally Posted by Mybowlcut

Could it be that buttons is a vector of objects whilst elements is a vector of object pointers? Unfortunately I can't really post a working example as my code uses a third party library.

---

No, that can't be it. As the clone function returns a pointer, the target should be a vector of pointers. As you are using mem_fun_ref, the source should be a vector of objects. Check my example.

Quote:

---

Originally Posted by Mybowlcut

Code:

---

    // Update screen elements.
    test_screen.Update(event_);
    // Draw(blit) elements to screen.
    test_screen.Draw(DE.Get_Screen());
    // Draw screen.
    DE.Draw_Screen();

---

In the real problem, they're going to be stored in a vector of base pointers (Base_XImage) which itself is stored in my Screen class. From there, each time Update or Draw gets called as above, each element in the vector of base pointers will have Update and Draw called polymorphically. The class hierarchy looks like this:

Code:

---

Base_XImage
  XImage
  XButton

---

---

Wait, what is the vector of base pointers going to be used for? Just to have a list of drawing objects that need to be updated? If that's the case, what happens if someone alters the original object? Are you expecting to see that change in the "cloned" vector?

Viggy

Quote:

---

Originally Posted by MrViggy

Wait, what is the vector of base pointers going to be used for? Just to have a list of drawing objects that need to be updated? If that's the case, what happens if someone alters the original object? Are you expecting to see that change in the "cloned" vector?

Viggy

---

The vector of base pointers holds images, buttons, etc. that can be drawn and updated, yes. I don't understand what you mean by alters the original object.

Code:

---

void Screen::Load(const std::string& directory)
{
  std::ifstream image_file;
  IO::open_read_file(image_file, directory + IMAGES_FN);
 
  const std::vector<XImage>& images =
    IO::read_data<XImage, std::vector<XImage> >(image_file);

  /*std::transform(images.begin(), images.end(),
    std::back_inserter(elements), (std::mem_fun_ref(&Base_XImage::Clone)));*/

  std::vector<XImage>::const_iterator image_it = images.begin();
  for(; image_it != images.end(); ++image_it)
  {
    elements.push_back(new XImage(*image_it));
  }

  image_file.close();
  std::ifstream button_file;
  IO::open_read_file(button_file, directory + BUTTONS_FN);

  const std::vector<XButton>& buttons =
    IO::read_data<XButton, std::vector<XButton> >(button_file);

  /*std::transform(buttons.begin(), buttons.end(),
    std::back_inserter(elements), (std::mem_fun_ref(&Base_XImage::Clone)));*/

  std::vector<XButton>::const_iterator button_it = buttons.begin();
  for(; button_it != buttons.end(); ++button_it)
  {
    elements.push_back(new XButton(*button_it));
  }

  button_file.close();
  std::ifstream audible_button_file;
  IO::open_read_file(audible_button_file, directory + AUDIBLE_BUTTONS_FN);

  const std::vector<Audible_XButton>& audible_buttons =
    IO::read_data<Audible_XButton, std::vector<Audible_XButton> >(audible_button_file);

  /*std::transform(audible_buttons.begin(), audible_buttons.end(),
    std::back_inserter(elements), (std::mem_fun_ref(&Base_XImage::Clone)));*/

  std::vector<Audible_XButton>::const_iterator audible_button_it = audible_buttons.begin();
  for(; audible_button_it != audible_buttons.end(); ++audible_button_it)
  {
    elements.push_back(new Audible_XButton(*audible_button_it));
  }

  audible_button_file.close();
}

---

That's my code... it's appalling, I know. :rolleyes: I need to sort it out so there's no duplication, but I'm trying to show you what I'm doing. If read_data could return a vector of pointers to newed objects then I'd use that instead of this whole copying thing.

Code:

---

// Reads data from a file.
  //  - Requires that Object has an overloaded >> operator.
  //  - Returns a Container of Objects.
  template <typename Object, typename Container>
  Container read_data(std::istream& file)
  {
    Container v;

    std::copy(
      std::istream_iterator<Object>(file),
      std::istream_iterator<Object>(),
      std::back_inserter(v));

    return v;
  }

---

What I mean is that your vector of base pointers is a copy of the original object. That means if some other piece of code updates the original object, you won't be drawing the object correctly.

Having said that, it looks like your code is okay. The list of original objects (the ones you are making copies of) is destroyed anyway. So, nevermind. :)

Viggy

If I understand your problem correctly, the smartest thing to do is to read directly from the istream into a vector of pointers, something for which you would need a custom iterator. The following was quickly hacked based on the std::back_inserter in my STL implementation (thus I am not 100% sure it only uses the STL public interface and will run on any STL implementation):

Code:

---

template<typename _Container>
class clone_back_insert_iterator
  : public std::iterator<std::output_iterator_tag, void, void, void, void>
{
protected:
  _Container* container;
 
public:
  typedef _Container container_type;

  explicit
  clone_back_insert_iterator(_Container& __x) : container(&__x) { }
 
  template<typename _ValueType>
  clone_back_insert_iterator& operator=(_ValueType __value)
  {
    container->push_back(new _ValueType(__value));
    return *this;
  }

  clone_back_insert_iterator& operator*()
  { return *this; }

  clone_back_insert_iterator& operator++()
  { return *this; }

  clone_back_insert_iterator operator++(int)
  { return *this; }
};

template<typename _Container>
inline clone_back_insert_iterator<_Container> clone_back_inserter(_Container& __x)
{ return clone_back_insert_iterator<_Container>(__x); }

---

With this, you should be able to use std::copy to copy objects from any stream or container to a vector of (base class) pointers:

Code:

---

#include <vector>
#include <algorithm>
#include <functional>

class Base
{
public:
  virtual Base * clone() const = 0;
  virtual ~Base() {}
};

class Derived : public Base
{
public:
  virtual Derived * clone() const { return new Derived(*this); }
  virtual ~Derived() {}
};

int main()
{
  std::vector<Derived> v1(3);

  std::vector<Base*> v2;
  std::copy(v1.begin(), v1.end(),
            clone_back_inserter(v2));
}

---

Looks great, treuss. Where did you put that code? I should put it in my own header file (not in <istream>!), shouldn't I?

Quote:

---

Originally Posted by Mybowlcut

Looks great, treuss. Where did you put that code? I should put it in my own header file (not in <istream>!), shouldn't I?

---

In its own header file and probably into some namespace as well.

Ok.

I've got some errors from your code...

Code:

---

Error        1        error C4980: '__value' : use of this keyword requires /clr:oldSyntax command line option        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        19
Error        2        error C2327: 'Clone_Back_Insert_Iterator<_Container>::container' : is not a type name, static, or enumerator        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        16
Error        3        error C2065: '__x' : undeclared identifier        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        16
Error        4        error C3861: 'container': identifier not found        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        16
Error        5        error C2656: 'Clone_Back_Insert_Iterator<_Container>::clone_back_insert_iterator' : function not allowed as a bit field        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        16
Error        6        error C2071: 'Clone_Back_Insert_Iterator<_Container>::clone_back_insert_iterator' : illegal storage class        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        16
Error        7        error C4430: missing type specifier - int assumed. Note: C++ does not support default-int        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        16
Error        8        error C2143: syntax error : missing ';' before '&'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        19
Error        9        error C4430: missing type specifier - int assumed. Note: C++ does not support default-int        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        19
Error        10        error C2238: unexpected token(s) preceding ';'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        19
Error        11        error C2059: syntax error : '__value'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        19
Error        12        error C4430: missing type specifier - int assumed. Note: C++ does not support default-int        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        19
Error        13        error C2143: syntax error : missing ';' before '<end Parse>'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        19
Error        14        error C2334: unexpected token(s) preceding '{'; skipping apparent function body        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        26
Error        15        error C2143: syntax error : missing ';' before '&'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        28
Error        16        error C4430: missing type specifier - int assumed. Note: C++ does not support default-int        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        28
Error        17        error C4430: missing type specifier - int assumed. Note: C++ does not support default-int        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        29
Error        18        error C2988: unrecognizable template declaration/definition        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        29
Error        19        error C2059: syntax error : 'return'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        29
Error        20        error C2238: unexpected token(s) preceding ';'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        29
Error        21        error C2146: syntax error : missing ';' before identifier 'clone_back_insert_iterator'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        31
Error        22        error C2143: syntax error : missing ';' before '<'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        36
Error        23        error C2433: 'clone_back_insert_iterator' : 'inline' not permitted on data declarations        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        36
Error        24        error C4430: missing type specifier - int assumed. Note: C++ does not support default-int        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        36
Error        25        error C2988: unrecognizable template declaration/definition        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        36
Error        26        error C2059: syntax error : '<'        c:\documents and settings\user\my documents\visual studio 2005\projects\sdl_game_engine\sdl_game_engine\clone_back_insert_iterator.h        36

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What's this?

Code:

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template<typename _Container>
inline clone_back_insert_iterator<_Container> clone_back_inserter(_Container& __x)
{
        return clone_back_insert_iterator<_Container>(__x);
}

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Also, if I were to summarise the class, what should I say? I've written this:

Code:

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// Template class for dynamically creating/storing objects.

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But it sounds too general...

Also... :rolleyes: I've got this function, and I copied it for Clone_Back_Insert_Iterator... just wondering if the second one (new one) is correct:

Code:

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                // Reads data from a file.
        //        - Requires that Object has an overloaded >> operator.
        //        - Returns a Container of Objects.
        template <typename Object, typename Container>
        Container read_data(std::istream& file)
        {
                Container v;

                std::copy(
                        std::istream_iterator<Object>(file),
                        std::istream_iterator<Object>(),
                        std::back_inserter(v));

                return v;
        }

        // Same as read_data, except stores newed objects.
        template <typename Object, typename Container>
        Container read_data_clone(std::istream& file)
        {
                Container v;
                std::copy(
                        std::istream_iterator<Object>(file),
                        std::istream_iterator<Object>(),
                        Clone_Back_Insert_Iterator(v));
        }

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Quote:

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Originally Posted by Mybowlcut

Ok.

I've got some errors from your code...

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As mentioned, the implementation is a copy & paste from my version of the STL. Start with removing all underscores at the beginning of variable names. I am also not sure, if the new iterator has to inherit the std::iterator, so if the inheritance gives you trouble, try removing it.

Quote:

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Originally Posted by Mybowlcut

What's this?

Code:

---

template<typename _Container>
inline clone_back_insert_iterator<_Container> clone_back_inserter(_Container& __x)
{
        return clone_back_insert_iterator<_Container>(__x);
}

---

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It's the function that allows you to write clone_back_inserter(v) instead of clone_back_insert_iterator<std::vector<Object *> >(v)

Quote:

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Originally Posted by Mybowlcut

Also, if I were to summarise the class, what should I say? I've written this:

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Insert iterator class that automatically allocates copies of the objects to be inserted on the heap.

Quote:

---

Originally Posted by Mybowlcut

Also... :rolleyes: I've got this function, and I copied it for Clone_Back_Insert_Iterator... just wondering if the second one (new one) is correct:

Code:

---

                // Reads data from a file.
        //        - Requires that Object has an overloaded >> operator.
        //        - Returns a Container of Objects.
        template <typename Object, typename Container>
        Container read_data(std::istream& file)
        {
                Container v;

                std::copy(
                        std::istream_iterator<Object>(file),
                        std::istream_iterator<Object>(),
                        std::back_inserter(v));

                return v;
        }

        // Same as read_data, except stores newed objects.
        template <typename Object, typename Container>
        Container read_data_clone(std::istream& file)
        {
                Container v;
                std::copy(
                        std::istream_iterator<Object>(file),
                        std::istream_iterator<Object>(),
                        Clone_Back_Insert_Iterator(v));
        }

---

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As mentioned above, use clone_back_inserter(v) as third argument. Besides, there is the tiny inconvenience that you are copying into a local variable, creating a huge memory leak once the function finishes and v goes out of scope. But I'm sure you would have noticed that sooner or later ;)

Quote:

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Originally Posted by treuss

As mentioned, the implementation is a copy & paste from my version of the STL. Start with removing all underscores at the beginning of variable names. I am also not sure, if the new iterator has to inherit the std::iterator, so if the inheritance gives you trouble, try removing it.

It's the function that allows you to write clone_back_inserter(v) instead of clone_back_insert_iterator<std::vector<Object *> >(v)
Insert iterator class that automatically allocates copies of the objects to be inserted on the heap.
As mentioned above, use clone_back_inserter(v) as third argument. Besides, there is the tiny inconvenience that you are copying into a local variable, creating a huge memory leak once the function finishes and v goes out of scope. But I'm sure you would have noticed that sooner or later ;)

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Ah... yes... huge memory leak. Haha! Is this a correct... correction? :p

Code:

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// Insert iterator class that automatically allocates copies
  // of the objects to be inserted on the heap.
  template <typename Object, typename Container>
  Container* read_data_clone(std::istream& file)
  {
    Container* v = new Container;

    std::copy(
      std::istream_iterator<Object>(file),
      std::istream_iterator<Object>(),
      Clone_Back_Inserter(v));

    return v;
  }

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Or perhaps should I have a Container& as a parameter? Like I (think) I said, I'm fairly new to using new! Puns mania around here... :sick:

Ok. I've fixed up the code like you suggested:

Code:

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#ifndef CLONE_BACK_INSERT_ITERATOR_H
#define CLONE_BACK_INSERT_ITERATOR_H

// Template class for dynamically creating/storing objects.
template<typename Container>
class Clone_Back_Insert_Iterator
  : public std::iterator<std::output_iterator_tag, void, void, void, void>
{
protected:
  Container* container;
 
public:
  typedef Container container_type;

  explicit
  Clone_Back_Insert_Iterator(Container& c) : container(&c) { }
 
  template<typename Element>
  Clone_Back_Insert_Iterator& operator=(Element e)
  {
    container->push_back(new Element(e));
    return *this;
  }

  Clone_Back_Insert_Iterator& operator*()
  { return *this; }

  Clone_Back_Insert_Iterator& operator++()
  { return *this; }

  Clone_Back_Insert_Iterator operator++(int)
  { return *this; }
};

template<typename Container>
inline Clone_Back_Insert_Iterator<Container> Clone_Back_Inserter(Container& c)
{
  return Clone_Back_Insert_Iterator<Container>(c);
}

#endif

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Just wanting to get the final OK before I use it in my code. It compiles fine.

Cheers for your help so far... it has been very useful. :thumb:

Quote:

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Originally Posted by Mybowlcut

Or perhaps should I have a Container& as a parameter?

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Preferably. That way, the calling function can decide whether to create the container on the heap or on stack.

Quote:

---

Originally Posted by Mybowlcut

Just wanting to get the final OK before I use it in my code. It compiles fine.

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Looks fine to me. I'm still not sure, if inheriting from std::iterator is necessary (or recommended). But there is certainly a is-a relationship, so why not if it works.

Quote:

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Originally Posted by treuss

Preferably. That way, the calling function can decide whether to create the container on the heap or on stack.
Looks fine to me. I'm still not sure, if inheriting from std::iterator is necessary (or recommended). But there is certainly a is-a relationship, so why not if it works.

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After several days of laziness and avoiding the whole thing, I got it to work. :) Thankyou! :thumb: