Problem with standard in copy/ostream_iterator

[Adalte]

Hi !
When I compile this piece of code I get the following error:
"NewShapes.cpp: In function `int main()':
NewShapes.cpp:12: error: `ShapePtr' cannot appear in a constant-expression
NewShapes.cpp:12: error: template argument 1 is invalid
NewShapes.cpp:12: error: template argument 2 is invalid"

I may change all code but not change the code in main (sorry), I may add code to the main but not change it.

NewShapes.cpp:

#include <vector>
#include <fstream>
#include <string>
#include "Vertex.h"
#include "Shape.cpp"
#include "Listan.h"
using namespace std;
 
main() {
  cout << endl;
  Listan ShapePtr;
  vector<ShapePtr> shapevec;
  Vertex varr[] = { Vertex(0,0), Vertex(10,0), Vertex(5,2), Vertex(5,5) };
  shapevec.push_back( shapePtr(new Polygon(1, 4, varr, 4)) );
  shapevec.push_back( shapePtr(new Circle(5, 5, 4)) );
  shapevec.push_back( shapePtr(new Rectangle(4, 10, 2, 4)) );
  shapevec.push_back( shapePtr(new Point(6, 7, 1)) );
 
  ofstream is("fil.dat");
  ostream_iterator<const shapePtr> shapeout(os, "\n");
  copy( shapevec.begin(), sahpevec.end(), shapeout);
  os.close();
 
  ifstream is("fil.dat");
  for (list<shapePtr>::iterator it = shapelist.begin(); it != shapelist.end(); it++)
      cout << *it << endl;
  shapevec.insert( shapevec.end(), shapelist.begin(), shapelist.end() );
 
  shapevec.erase(remove_if( shapevec.begin(), shapelist.end(), CloseTo( Vertex(6, 7)) ), shapevec.end() );
  ostream_iterator<const shapePtr>sahpeout(cout, "\n");
  cout << sahpevec.size() << endl;
  cerr << shapePtr::numshapes << endl;
  copy( shapevec.begin(), shapevec.end(), shapecout );
 
  cout << endl;
  return 0;
}
 

I attached the complete code.
Thank You for hints and help.

Adalte.

[Banfa]

The error messages highlight the problem

   Listan ShapePtr;
   vector<ShapePtr> shapevec;

You have passed ShapePtr as a template parameter but template parameters need to be types on the whole or occasionally constant values (const int, const float etc).

The error messages say all this. It is worth reading about and understanding the diagnostic message produced by your compiler.

[weaknessforcats]

Also, you do not #include .cpp files.

What you do is ADD .cpp files to your project. Each .cpp file must be compiled separately. The makefile takes care of compiling each .cpp file.

By #including .cpp files, you duplicate the code each time you compile. AT some point youo will start gettingr redefinition errors and your builds will stop working.

[Adalte]

Thank you for hints.
Manfa, you mean: "vector<const ShapePtr> shapevec"? Thats not work ...
weaknessforcats, all CPP compiles: there are just two, the others headers has inline code.

The problem still there ... Plaese help ...

Adalte.

[Adalte]

Hi !

I change the code. Now I get the following error:
"NewShapes.cpp:11: error: no matching function for call to `ShapePtr::ShapePtr(Polygon*)'"

How I can to put shapes (Polygons, Rectangles, etc) in the vector shapevec, how the code like, I wander.

Main:

#include <vector>
#include <fstream>
#include <string>
#include "Vertex.h"
#include "ShapePtr.cpp"
using namespace std;
 
main() {
  vector<ShapePtr> shapevec;
  Vertex varr[] = { Vertex(0,0), Vertex(10,0), Vertex(5,2), Vertex(5,5) };
  shapevec.push_back( ShapePtr(new Polygon(1, 4, varr, 4)) );
  ...
 

The class ShapePtr.h (I change name Shape (h and cpp) to ShapePtr):

#ifndef SHAPEPTR_H
#define SHAPEPTR_H
#include <iostream>
#include <string>
#include "Vertex.h"
using namespace std;
 
class ShapePtr {
  public:
    ShapePtr() {}
    ~ShapePtr() {}
};
#endif
 

ShapePtr.cpp:

#include <iostream>
#include <cmath>
#include "Vertex.h"
#include "ShapePtr.h"
using namespace std;
 
class Polygon : public ShapePtr {
  private:
    Vertex* Pol;
    int storlek, pX, pY;
  public:
    Polygon::Polygon(int x = 0, int y = 0, Vertex* varr = 0, int num = 0) : pX(x), pY(y), storlek(num) {
<< pY << endl;
      if (storlek > 0) {
         Pol = new Vertex[storlek];
         for (int ix=0; ix<storlek; ix++)
             Pol[ix] = varr[ix];
       } else Pol = 0;
    }
    virtual Polygon::~Polygon() { delete[] Pol; }
};
 

Help me, please.

Adalte.

[newb16]

Why do you inherit Polygon from ShapePtr? As I understand, you need to implement ( or use the already implemented ) shared pointer class, create a vector<shared_ptr<Shape> >;
and inherit polygon and other shapes from basic class Shape, so that the vector contains elements of the same type.

[weaknessforcats]

Thats not work ...
weaknessforcats, all CPP compiles: there are just two, the others headers has inline code.

Again, do not #include .cpp files.

It doesn't work.

Example:

X. cpp
 
int data = 10;
 
Y.cpp
#include "X.cpp"
 
Z.cpp
#include "Y.cpp"
int main()
{
 
}

This dies in the link with a redefinition of int data.

All files that you #include cannot: a) allocate memory or b) contain any code that causes the compiler to generate instructions. You #include files that cotain only declarations rather than definitions.

[Banfa]

I think in this case the mistake is not in including a cpp file (which is a mistake and should not be done) but in the file name itself.

Examining the code in the cpp file being included it is apparent that it contains a class declaration, that is statements you would normally expect to find in a header file. The mistake is in giving what is basically a header file the .cpp extension.

If you want to have a vector of polymorphic types, that is a vector of objects that exhibit the same interface but differences in how each concrete object implements the functionality you need to have a vector of pointers to some base class that all your polymorphic objects inherit from.

ShapePtr could be your base class and Polygon does inherit from it, there are some problems with this, shape pointer does not define an object interface (there are no virtual functions) and if you are intending that a class is to be used as the base of an inheritance tree of polymorphic types that will be accessed through a base class pointer then the destructor MUST be declared virtual.

Also instead of creating a vector of base class pointers you declare a vector of base classes. None of the objects in you vector will/can have the functionality of any of the derived classes (Polygon) because the base, ShapePtr, does not implement that functionality and you are storing the base class not a base class pointer to a derived class.

This code construct

ShapePtr(new Polygon(1, 4, varr, 4))

should be a give away that something is wrong. Polygon is derived from ShapePtr so I could do this legally

Polygon *pg = new Polygon(1, 4, varr, 4);
ShapePtr *ptr = pg;
 
// or indeed this
 
ShapePtr obj(static_cast<ShapePtr>(pg));
 

The last of those is fairly pointless in this case because ShapePtr has no data members to copy so it is actually the equivalent of

ShapePtr obj;

in this specific case.

I suspect you need to do the following:

1. Declare shapevec as

vector<ShapePtr *> shapevec;

2. Alter the declaration of ShapePtr to actually declare your polymorphic interface in it.

[Adalte]

Hi !

Thank You for hints.
The .cpp files are now not included.

Newb16, I'm not sure I understand You but I think it's my fault: I changed the classes name from Shape to ShapePtr, I'm sorry that I confuse You. I try to create a vector (named shapevec) and put there some shapes (polygons, rectangles, etc). Then I'll be sort them, remove some (according to size or position), save them on a file and read them from file.

I'm just in the beginning of this task, please help me.
Thank You in advance.

Adalte.

[Adalte]

Hi !

Banfa You are right. I implement a base class, ShapePtr.h, from other project and shapes (polygons, rectangles, etc) inherits (in ShapePtr.cpp) from it.

I solvet the problem. The constructor I need was:
ShapePtr(ShapePtr* ptr)
... its look like to work.

I'm in the beginning of this task, please help me. I started an other thread to continue there: "Help, please".

Thank You in advance.

Adalte.

[Adalte]

Hi !

I try to save a shapes from a vector to a file. When I compile a code I get a very large error that begin:

"C:/Qt2009_02/mingw/bin/../lib/gcc/mingw32/3.4.2/../../../../include/c++/3.4.2/bits/stream_iterator.h: In member fu
nction `std::ostream_iterator<_Tp, _CharT, _Traits>& std::ostream_iterator<_Tp, _CharT, _Traits>::operator=(const _Tp&) [wi
th _Tp = const ShapePtr, _CharT = char, _Traits = std::char_traits<char>]':" ...

Here is Main (NewShapes.cpp):

#include <vector>
#include <fstream>
#include <iterator>
#include <string>
#include "Vertex.h"
#include "ShapePtr.cpp"
using namespace std;
 
main() {
  vector<ShapePtr> shapevec;
cout << "  Main_BeforeVertices" << endl;
  Vertex varr[] = { Vertex(0,0), Vertex(10,0), Vertex(5,2), Vertex(5,5) };
  shapevec.push_back( ShapePtr(new Polygon(1, 4, varr, 4)) );
  shapevec.push_back( ShapePtr(new Circle(5, 5, 4)) );
  shapevec.push_back( ShapePtr(new Rectangle(4, 10, 2, 4)) );
  shapevec.push_back( ShapePtr(new Point(6, 7, 1)) );
 
  ofstream os("fil.dat");
  ostream_iterator<const ShapePtr> shapeout(os, "\n");
  copy(shapevec.begin(), shapevec.end(), shapeout);
  os.close();
}
 

What I'm missing, I wander.
Thank You in advance.

Adalte.

Pd: I attached the files with code (NewShapes.cpp, ShapePtr.h, ShapePtr.cpp, Vertex.h) and full error message.

[Banfa]

Adalte,

I have renamed this thread, we prefer our threads to have meaningful names and "I need help" has no meaning in relation to the problem. You should probably take a little time to read our posting guidelines.

I have merged your other thread into this one since it is not really a separate problem.

You have not taken on board what has been said about icluding files. If the file is written to be included into other files then it should not have a .cpp extension but a .h extension.

We can not help you with an error message if you only post half of it.

Even if your code compiled I would be surprised if you ended up with any data in your output file because the class ShapePtr has no data in it.

You have not taken on board what I said about vectors and the type you are storing in the vector in your code.

[donbock]

@Banfa
This file naming convention is not required by the language standard but there is near universal compliance within the user community. Violating this convention assures maximum confusion when others look at your code.

[Adalte]

@Banfa
Right. Do You can rename it to something like "Problem with standard in copy/ostream_iterator", please?

@Banfa
I agreed with donbock. I didn't think about it but about the self problem. The extension name is correct now.

@Banfa
I don't understand it. In my last post, I write that I solve the first problem, I write the code (solution) and I attach a file with all error message. You can read that post.

@Banfa
If You are right, may be it can help me. May be You can explain it for me. I check that the ShapePtr's constructor is called after I put each shape (4 shapes, 4 calls) and ShapePtr's destructor is called (4 times) before the program is terminated.

@Banfa
May be You forgot what I wrote in my first post: I can not change the code in main but I may add a new code to the main. I may change, delete and add code to the others files.

My problem now is copy-command. If I remark it, the code compiles without errors else with very large error.

I attached the files.

It's the main (NewShapes.cpp) now:

#include <vector>
#include <fstream>
#include <iterator>
#include <algorithm>
#include <string>
#include "Vertex.h"
#include "Shapes.h"
using namespace std;
 
int main() {
  vector<ShapePtr> shapevec;
  Vertex varr[] = { Vertex(0,0), Vertex(10,0), Vertex(5,2), Vertex(5,5) };
  shapevec.push_back( ShapePtr(new Polygon(1, 4, varr, 4)) );
  shapevec.push_back( ShapePtr(new Circle(5, 5, 4)) );
  shapevec.push_back( ShapePtr(new Rectangle(4, 10, 2, 4)) );
  shapevec.push_back( ShapePtr(new Point(6, 7, 1)) );
  ofstream os("fildat.txt");
  ostream_iterator<const ShapePtr> shapeout(os, "\n");
 
  copy(shapevec.begin(), shapevec.end(), shapeout); //  <-- !!!
 
  os.close();
}
 

Adalte.

[donbock]

@Adalte
It is not uncommon to have the constraint that a certain preexisting file can't be changed; but neither of the more common reasons for that constraint seem to apply in your case.

1. The most common reason is that the source file has been lost. That obviously isn't the case.
2. Sometimes a source file belongs to somebody else and there are legal reasons why you can't alter it. However, you're willing to "add new code".

How do you perceive the distinction between changing the code and adding new code? Are you saying that you are allowed to intersperse new lines among the original lines, but that you could reconstitute the original file merely be deleting the new lines? Are you allowed to effectively delete original lines by bracketing them with "#if 0" and "#endif"? What is the underlying reason for this constraint?

[newb16]

@donbock
The reason is to force students to use specific constructions, i.e. ostream_iterator, and implement operator << for their specific class to make ostream_iterator compile. Without this restriction, they will just loop through the container and invoke some TheirClass::output() method for each element.

[Banfa]

@Adalte
Are you saying you get errors? If so post them in full.

Sorry forgot about not being able to change main but given that you have a vector of ShapePtr objects so when you do this

shapevec.push_back( ShapePtr(new Polygon(1, 4, varr, 4)) );

what do you think happens, explain it in English (or, for your own purposes only, in your first language if that is not English)? What happens in the ShapePtr object created when it is initialised from the Polygon? What do you think gets put into the vector?

Read the documentation for ostream_iterator, if you want to be able to do this

[/code]
ostream_iterator<const ShapePtr> shapeout(os, "\n");

copy(shapevec.begin(), shapevec.end(), shapeout); // <-- !!!
[/code]

the this

cout << ShapePtr;

has to be valid. Is that valid for your code? If it was valid what data would be being output for ShapePtr?


And a final point, although this is not preventing the code from working and it is in main so not code written by yourself but if you new something then at some point you should delete it before the program exits.

[Adalte]

Sorry but my english is not so god.

@Banfa
I did. You can see it in my attached files: error.txt

@Banfa
I see what You mean: ShapePtr's defaultconstructor is called, then Polygon's constructor, then Vertex's constructor, then ShapePtr's constructor and last ShapePtr's destructor: Here is the problem. Why ShapePtr's destructor is called here I don't understand. How I can avoid it?

@Banfa
I have read it and read the examples: The syntax is the same but with an other variables names. Or ...?

What do You think I have to do to keep the objects in the vector, so that I can save them in a file?

Adalte.

[weaknessforcats]

I see what You mean: ShapePtr's defaultconstructor is called, then Polygon's constructor, then Vertex's constructor, then ShapePtr's constructor and last ShapePtr's destructor: Here is the problem. Why ShapePtr's destructor is called here I don't understand. How I can avoid it?

The destructor of ShapePtr is called because you have a pointer to ShapePtr.

I realize that if you really have the address of a Polygon in your ShapePtr that you should be calling the Polygon destructor instead.

You make this happen by using a virtual destructor in the ShapePtr class.

Actually, you should have a Shape class:

class Shape
{
 
    public:
       virtual ~Shape();                //virtual destructor
};
class Polygon: public Shape
{
 
};

rather than ShapePtr. Your polygon is:

Shape* myShape = new Polygon();

and your vector of shapes is a vector of Shape pointers:

vector<Shape*> myShapes;
myShapes.push_back( new Polygon());

[Banfa]

@weaknessforcats
If you read the thread (and it is long and converluted so I undersand why you didn't) you would see we have already had this argument, however he can not change the main.cpp where the vector is defined as

vector<ShapePtr> myShapes;

Personally I think it is a mistake to subclass from ShapePtr, I think there should be a different base class and that ShapePtr should be written in the form of the Handle Pattern to hold that other base class pointer.

ShapePtr would then also need the methods required to let the ostream_iterator to work.

[Adalte]

weaknessforcats, banfa let's go: we try weaknessforcats idea. But weaknessforcats may should read my last uploaded files: there is not Shape class, may be You mean ShapePtr?
Then, You write:

Shape* myShape = new Polygon();
vector<Shape*> myShapes;
myShapes.push_back( new Polygon());
 

1. Mean You an empty Polygon() ?
2. What does Your pointer "myShape" ? (Sorry, I don't get it)
3. If we will put pointers of shapes (Polygon, Rectangle, etc) into the vector, why we need pointers to that shapes and do nothing with them? Or You mean
4. If we will have "vector of shapes is a vector of Shape pointers", isn't the code as follow?:

ShapePtr* myShape = new Polygon();
vector<ShapePtr*> shapesvec;
shapevec.push_back(myShape);
 

Please, understand me right: I try to understand what You two mean, which I appreciate it and thank very much.

Adalte.