Making an array of pointer to classes

Question

I am trying to make an Array which will contain pointer to a class. The size of the array will be given from keyboard , so i tried to create the array with the following way :

 class creature
 {
    protected:
      string crt_name ;
      int L ;   
    public:
       creature( int Life = -1 , string Name = "")
        : L(Life) , crt_name(Name){} 

       string get_crt_name ( void )
       { 
          return crt_name ;
       }
 }; 

 class creature_society
 {
    private:
       creature* *A ;
       int noc ;
    public:
       creature_society( int , int ) ;
       ~creature_society() ;
       creature** get_A ( void ){return A ;}
 };

The constructor of creature society will fill the array with creatures made randomly

creature_society::creature_society( int life , int number_of_creatures )
{
   noc =  number_of_creatures ;
   A = new creature*[noc] ;

   creature* temporary ;

   for( int  i = 0 ; i<= number_of_creatures -1 ; i++)
   {
     if ( rand()%100 <= 50) 
        {
            temporary = new good_creature( life , get_unique_name( 3 ) );
            A[i] = temporary ;
        }
        else
        {
            temporary = new bad_creature( life , get_unique_name( 3 ) );
            A[i] = temporary ;
        }
  }
}

Then I try to print the array

    cout << endl << "Printing Society:" << endl ;
    for ( j = 0 ; j <= N -1 ; j++)
    {
       temp = (*( cs1.get_A() + j ))->get_crt_name() ;
    }

The problem is that when i am getting segmentation faults when running on linux , while working fine on Dev C++ ( most of the time )! Any mistakes you pointed out ?

Are you opposed to `std::vector`? It will make your life a lot easier. — Cory Kramer, Dec 30 '15 at 13:37
@LightnessRacesinOrbit Okay fine, even better would be `std::vector>`. Baby steps :) — Cory Kramer, Dec 30 '15 at 13:39
@CoryKramer: Let's not give the super-sharp axe to a baby, eh? :) — Lightness Races in Orbit, Dec 30 '15 at 13:39
@LightnessRacesinOrbit surely a raw pointer is the sharpest axe in the toolshed? Used only for the very hardest trees? — Richard Hodges, Dec 30 '15 at 13:58
You also forgot to define a virtual destructor in `creature` — n. m. could be an AI, Dec 30 '15 at 14:08
Eh, why any ptr? std::vector is the way to do it. Since there is no virtual destructor in creature, there is no need for the pointer. — SergeyA, Dec 30 '15 at 14:19
@SergeyA You'll notice they say `new good_creature` and `new bad_creature` later in the code. They'll [slice](https://stackoverflow.com/questions/274626/what-is-object-slicing) if they store them that way. — Cory Kramer, Dec 30 '15 at 15:12
@CoryKramer, and they will have a memory leak if they store it as a pointer to base... — SergeyA, Dec 30 '15 at 15:14
@SergeyA Not if they use `std::unique_ptr` and the base class has a `virtual` destructor. — Cory Kramer, Dec 30 '15 at 15:14
@CoryKramer, but there is none. I am talking about the code as written. — SergeyA, Dec 30 '15 at 15:17

score 0 · Answer 1 · answered Dec 30 '15 at 13:53

0

I think you can simply do,

for (int j=0 ; j < N; ++j)
{
   temp = cs1.get_A()[j]->get_crt_name();
}

answered Dec 30 '15 at 13:53

Pravar Jawalekar

605
1
6
18

Aviv · Answer 2 · 2015-12-30T14:13:09.550

0

You don't mention here the classes of bad_creature and good_creature. I assume they inherit creature as a base a class and therefore you should define get_crt_name as a virtual function.

Maybe something went wrong with your get_unique_name function as well. I executed your code in VC2015 and no faulty was found (I replaced ofcourse good creature and bad creature classes with creature and that I replaced get_unique_name with a const string).

Please:

1.Check with your core dump where did your program crash. 2.What output it emitted before the segmentation fault.

For future, class names should always begin with uppercase letters as it is a very common style convention.

edited Dec 30 '15 at 14:13

answered Dec 30 '15 at 14:05

Aviv

414
4
16

@CoryKramer I will edit my answer accordingly, though I really hate to encounter classes definitions starting with lowercase letters.. (unless they are from std of course) – Aviv Dec 30 '15 at 14:11
I encounter a weird problem guys , – Social Programmer Dec 30 '15 at 19:45
@Social Programmer well, can't help if you don't write them down – Aviv Dec 30 '15 at 22:57

Making an array of pointer to classes

2 Answers2