Is it possible to have a class with an array of class objects from another class inside?

Question

I have a class called Regions and another class I will call Area. In the main class Area, I need to have an array of Region class objects.

Here is my region class:

class Region 
{
public:

    // Constructor
    Region();

    // Get/set functions
    bool getPoly()              {return poly;}
    bool setPoly(bool value)    {poly = value;}
    long getMesh()              {return mesh;}
    void setMesh(long value)    {mesh = value;}
    long getVisibleNum()        {return visibleNum;}
    void setVisibleNum(long value)  {visibleNum = value;}

    // Visibility vector
    void reserveSpace();
    long addVisibleRegion(int region);
    long getSize(){return visibility.size();}

    friend class Area;

private:
    bool poly;          // Does the region have polygons?
    long mesh;          // The reference to a 0x36 mesh
    long visibleNum;    // The number of visible regions
};

Now in my area class, I am trying to declare something like this :

class Area
{
public: // Some public class functions
private:
Region* regionArray; // this should be pointers to an array of class objects
}

In the Area class constructor, I will allocate the number of class objects I want.

I am getting this error:

error C2143: syntax error : missing ';' before '*'
error C4430: missing type specifier - int assumed.
Note: C++ does not support default-int

So I assume I am not setting it up correctly. It worked perfectly when Region was a struct but now that it is a class, I assume I am doing something wrong.

How do you include the files, are they in different files, have you added the prototype of one class in the others header, etc. — Tommy Andersen, Jun 18 '11 at 00:50
The definition of `Area` is missing a semicolon after the closing brace. — fredoverflow, Jun 18 '11 at 00:54
Also, I strongly recommend using `std::vector` instead of `Region*`. This simplifies ensuring correct copying behavior of `Area` objects immensely. [related FAQ](http://stackoverflow.com/questions/4172722/) — fredoverflow, Jun 18 '11 at 00:55
`Region` is not in scope where you attempt to use it. Fortunately you'll only need a forward declaration. — Lightness Races in Orbit, Jun 18 '11 at 00:56

score 1 · Answer 1 · answered Jun 18 '11 at 00:52

Yes it is possible - do you have the classes defined in the same file? It sounds like they might be in separate files and you haven't included the header file for Region in the Area file.

Edit: Also, you have getter functions for the data in Region, so there is no need to make Area a friend of Region. I would also replace Region* regionArray with std::vector<Region> regionArray, so the memory is all managed for me.

score 1 · Answer 2 · answered Jun 18 '11 at 00:54

It seems to me that the problem is that you are referring to a class you have not yet defined. That is the: Region* regionArray; line in the Area class.

If this is the case you have to remember to include the header containing the Region class in the header file containing the Area class. Or add class Region; above the Area class.

Nawaz · Answer 3 · 2011-06-18T01:02:08.617

Yes, that is possible. In your case, the problem isn't array. but (most likely) you've not included some header files in some other files.

By the way, you can use std::vector as well, which in my opinion would be a better choice, in comparison to raw pointer.

#include <vector>
#include "Region.h" //must include these two

class Area
{
  public: // Some public class functions
  private:
  std::vector<Region> regions;  //better than raw pointer
};

Read about RAII Idiom : Resource Acquisition Is Initialization

score 0 · Answer 4 · answered Jun 18 '11 at 02:25

Other common problem is the friend class Area; declaration inside the class without a forward declaration first (I'm almost sure this is the case, are you using GCC?)

In Region.h

class Area;  // <- this is a forward declaration

clasee Region {
 ...
 friend class Area;
};

Regards

Is it possible to have a class with an array of class objects from another class inside?

4 Answers4