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Accessing of objects in an array

Posted on 2004-08-16
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I have an template which is an array that stores objects. To display all the objects of the array I wrote a code it is not working.  The code is as below. The displaying of the trucks is written in Agency class.

cout<<trucks; //code to display the trucks


trucks is a template of array to store trucks

FlexArray<Trucks*> trucks;// declaration of trucks template.(this declaration is also done in agenct class only)

The code for trucks and the template(Flexarray) is as below.
/////////////////////////////////////trucks.cpp//////////////////////////////////////////////////////////////

#include "Trucks.hpp"

Trucks::Trucks(char *a,int b,int c,bool avail)
{
      int len;
      len = strlen(a);

    Truck_Name = new char[len+1];
      
      strcpy(Truck_Name,a);
      Year=b;
      VIN=c;
      Available=avail;
}
      
Trucks::~Trucks()
{
   clog<<"Deleted Truck"<<Truck_Name<<endl;
   delete Truck_Name;

}

ostream& Trucks::print(ostream& out)
{
    if(Available)
            out<<setw(10)<<VIN<<setw(20)<<Truck_Name<<setw(10)<<Year<<setw(6)<<"Yes"<<endl;
      else
        out<<setw(10)<<VIN<<setw(20)<<Truck_Name<<setw(10)<<Year<<setw(6)<<"No"<<endl;
    return out;
}


////////////////////////////////flexarray.hpp/////////////////////////////////////////////////////////////////////

#ifndef FLEX
#define FLEX
 // ==========================================================================
 // Template declaration for a flexible array of base type T.

 #include "tools.hpp"
 #define FLEX_START 4 // Default length for initial array.

 template <class T>
 class FlexArray {
 private:// ---------------------------------------------------------------
 int Max;                  // Current allocation size.
 int N;                        // Number of array slots that contain data.
 T* Data;                  // Pointer to dynamic array of T.

 void grow(void);            // Double the allocation length.

 public: // ---------------------------------------------------------------
 FlexArray( int ss = FLEX_START ) : Max(ss), N(0), Data( new T[Max] ) {}
 //~FlexArray() { if (Data != NULL) delete[] Data; }
 ~FlexArray() { for (int i=0; i<N; i++) delete Data[i]; }

 int put( T data );
 const T find(int id){
       for(int i=0; i<N; ++i) {if(*Data[i]==id) return Data[i];}
       return NULL;

 }

 const T find(char* nm){
       for(int i=0; i<N; ++i) {if(*Data[i]==nm) return Data[i];}
       return NULL;

 }
 
T remove(int id)
{
      T temp;

      for(int i=0;i<N; i++)
      {
            if(*Data[i]==id) {temp=Data[i]; Data[i]=Data[--N]; delete temp;}
      }

      return NULL;
}

 T& operator[]( int k );

 int data_size() {return N;}

 T* extract() { T* tmp=Data; Data=NULL; Max = N = 0; return tmp; }
 ostream& print( ostream& out ) const
 {
      for (int k=0; k<N; ++k) out << Data[k] <<endl;
      return out;

 }
 };
 template <class T> inline ostream&
 operator<< ( ostream& out, FlexArray<T>& bp){ return bp.print(out); }

template <class T> int
 FlexArray<T>::put( T data ){
 if ( N >= Max ) grow(); // Create more space if necessary.
                        
 Data[N]= data;
 return ++N;            // Return subscript at which item was stored.
 }

 //------------------------------------------- access the kth T in the array.
 template <class T> T&
 FlexArray<T>::operator[]( int k ) {
 if ( k >= N ) fatal( "Flex_array bounds error." );
 return Data[k];      // Return reference to desired array slot.
 }

 // ------------------------------------- double the allocation length.
 template <class T> void
 FlexArray<T>::grow()
 {
      T* temp = Data;    // hang onto old data array.
      Max*=2 ;
      Data = new T[Max]; // allocate a bigger one.
      memcpy(Data, temp, N*sizeof(T)); // copy info into new array.
      delete temp;            // recycle (free) old array.
 }                  
 
#endif

0
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Question by:rmvprasad
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4 Comments
 
LVL 12

Expert Comment

by:andrewjb
ID: 11818409
Give us a clue. In what way doesn't it work?
0
 
LVL 4

Expert Comment

by:smpoojary
ID: 11818797
Don't show your actual code. Becuase we have no patience to read it.  
Please convert it to a simple example. After clear this simple example then you can convert it to your actual project code.

Let me know simple example for your doubt.
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 11820421
You have an array of pointers to objects. That means that T is of type Trucks*.

You find the object with one of the following:
--------8<--------
//...
const T find(int id){
      for(int i=0; i<N; ++i) {if(*Data[i]==id) return Data[i];}
      return NULL;
 }
const T find(char* nm){
      for(int i=0; i<N; ++i) {if(*Data[i]==nm) return Data[i];}
      return NULL;

 }
--------8<--------

That means that you would need to have Trucks::operator==(int) or Trucks::operator==(const char*) defined, which I do not see in your Trucks class definition. In any case I don't believe that it would be good style to have one of these defined.

May I suggest you take a step back and reconsider your design.

Is this an academic assignment or can you consider using a standard library container?
0
 
LVL 39

Accepted Solution

by:
itsmeandnobodyelse earned 200 total points
ID: 11821163
>> FlexArray<Trucks*> trucks

When using Trucks* as an template argument, you try to print a pointer Data[k] with that

    for (int k=0; k<N; ++k) out << Data[k] <<endl;

So you should change your array to

    FlexArray<Trucks> trucks;

However, after this you need a copy constructor as the array holds copies of Trucks objects

   Trucks::Trucks(const Trucks& tr)
         : Year(tr.Year), VIN(tr.VIN), Available(tr.Available) {}

Also, you need an operator<<  (instead of print), an operator = (to assign Trucks objects) and an operator == (to compare array objects with search object).

operator<< function normally is declared  as friend in class Trucks

    class Trucks
    {

            ...
    public:
            friend ostream& operator << (ostream& os, const Trucks& tr);
            ...
    };

and defined like that:

      ostream& operator<<(ostream& os, const Trucks& tr)
      {
             tr.print(os);
             return os;
      }

The other operator functions you should be able to implement yourself.

Regards, Alex
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