Array of objects dynamic memory allocation

Question

I'm trying to allocate dynamic memory to an array of objects, but I keep getting the following error:

"error: C2143: syntax error : missing ';' before '*'" "error: C2501: 'Figura' : missing storage-class or type specifiers"

Any help is welcomed. I'm using Visual Basic C++ 2006, but will switch to Turbo C++ 3.0 with Dosbox to get graphics.h working :( .

Here's the code:

#include<iostream.h>

class Grup {
    private:
        int nr_elemente;
        Figura *figuri;
    public:
        Grup() {
            figuri = new Figura[nr_elemente];
        }
};


class Figura {

public:
    Figura();
    ~Figura();
    Figura(const Figura&);

    friend Figura operator+(const Figura& fig1, const Figura& fig2) {};
    friend Figura operator+(const Grup& gr1, const Grup& gr2) {}

    friend Figura operator*(const Figura& fig) {}
    friend Figura operator*(const Figura& fig) {}

};

Figura operator+(const Figura& fig, const Grup& gr) {
    return fig;
}

class Punct : Figura
{
public:
    int x, y;

    Punct(int x, int y) {
        Punct::x = x;
        Punct::y = y;
    }
};

class Segment : Figura
{
public:
    int x, y, poz;
};

class Dreptunghi : Figura
{
public:
    int x, y, poz;
};

void main(void) {



}

Turbo C++ 3.0 is from 1991. Not recommended for anything.

Bo Persson
– Bo Persson

2012-04-23 18:29:22 +00:00
Commented Apr 23, 2012 at 18:29 — Bo Persson
– Bo Persson, Commented Apr 23, 2012 at 18:29

mfontanini · Accepted Answer · 2012-04-23 18:14:12Z

2

In this line:

figuri = new Figura[nr_elemente];

The compiler does not know that a class Figura exists. Therefore, it generates an error, since "Figura" is an unknown token at that point. You should use a forward declaration:

class Figura; // forward-declare class Figura

class Grup {
/* ... */
};


class Figura {
/* ... */
};

The problem is that the compiler does not know the size of a class Figura, therefore it can't allocate an array of objects of this type. Therefore you will probably need to use pointers or modify your class design.

answered Apr 23, 2012 at 18:14

mfontanini

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7 Comments

BebliucGeorge Over a year ago

Can you please give me an example of how can I use pointers instead of what I am doing now?

juanchopanza Over a year ago

Doesn't he need the complete Figura class for the call to new to work?

BebliucGeorge Over a year ago

Ok, i forward-declared Figura, but now getting "no appropriate default constructor available." at the line with figuri = new Figura[nr_elemente];

juanchopanza Over a year ago

@Bdesign you need to declare and define Figura before Grup as I said in my answer..

BebliucGeorge Over a year ago

Hmmm I think I should consider redesigning the classes a little.

|

Artak Begnazaryan · Accepted Answer · 2012-04-23 18:34:52Z

0

Your problem is that you're trying to do all in one file. You'll not have such kind of problems if you move the declaration and definition of classes to separate .hpp and .cpp files. Move

// file grup.hpp

class Figura; // forward declaration

class Grup {
private:
    int nr_elemente;
    Figura *figuri;
public:
    Grup();
};

to grup.hpp file. Then implement the constructor of Grup in group.cpp file:

// file grup.cpp
#include "grup.hpp"
#include "figura.hpp"


Grup::Grup()
{
    figuri = new Figura[nr_elemente];
}

Also move the definition and declaration of Figura class to corresponding figura.hpp and figura.cpp files. Better to use the same approach with all classes you have.

answered Apr 23, 2012 at 18:34

Artak Begnazaryan

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Comments

clanmjc · Accepted Answer · 2012-04-26 17:47:51Z

0

You need to forward declare, already mentioned, but that is not enough, you need to know the size of the class in order to use it as an implementation. Therefore...

class Figura;
class Grup{
  Figura * figuri;
  //.. other stuff, but ONLY declarations no implementations.
};

class Figura
{
  //Same as you already have...
};

After the classes have been declared, since they are in the same file you need to implement AFTER the other classes have been implemented (or declared).

//Still same file but below the Figura class definition..
Grup::Grup() {
   //Now you can use Figura...
   figuri = new Figura[nr_elemente];
}

@be The problem you are seeing with your comment below has to do with the assignment operator for your fig class.

The operator looks like this... Fig& operator=(const Fig& );

But with your example you are assigning a pointer void func(const Fig * fig) { //... figcontainer[index] = fig; // if you did *fig; you would be ok //...
}

edited Apr 26, 2012 at 17:47

answered Apr 23, 2012 at 19:00

clanmjc

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1 Comment

BebliucGeorge Over a year ago

I did a little redesigning and now almost everything works. The only problem is I think I'm not doing the dynamic memory allocation right. I get : error C2679: binary '=' : no operator defined which takes a right-hand operand of type 'class Figura *' . The line is : void adauga_element(Figura *fig) { figuri[nr_elemente++] = fig; } .

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