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C++ class template problem

Posted on 2010-11-13
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Last Modified: 2012-05-10
I am experimenting with templates in C++ using Borland C++ Builder.
I have used STL quite successfully in the past and I have encountered a problem in using a simple class template that I have written myself.

The code snipplet shows my header file and the cpp file.
The compile-time error occurs when compiling the header file with the following error message:

[C++ Error] Unit1.h(25): E2293 ) expected
 

The error refers to the line of code where the x member is declared in the Form1 class.

If I move the declaration of x from the Form1 header to the initialisation code in the constructor for Form1 however, no error is reported. (As per the code that is shown that is commented out).

Is is possible to declare a variable x of type Vtor<int> in the header of Form1 with a size of 5 ?



// header file Unit1.h

#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>

template <class T> class Vtor
{
   T *data;
   int size;
public:
   Vtor(int);
   ~Vtor( ) { delete[ ] data; }
   T& operator[ ] (int i) { return data[i]; }
};
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:	// IDE-managed Components
private:	// User declarations
   Vtor<int> x(5);   // Generate a vtor to store five integers

public:		// User declarations
    __fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

// cpp file Unit1.cpp
#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;

template <class T> Vtor<T>::Vtor(int n)
{
   data = new T[n];
   size = n;
};

//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
//  Vtor<int> x(5);
  for (int i = 0; i < 5; ++i)
      x[i] = i;              //  Initialize the vector.
}
//---------------------------------------------------------------------------

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Question by:alcindor
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Accepted Solution

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Infinity08 earned 500 total points
ID: 34127627
You can't initialize the data member there.

I assume you meant something like this (left out irrelevant stuff) :
class TForm1 : public TForm
{
private:
   Vtor<int> x;                      // <--- definition

public:
    TForm1() : x(5) { }              // <--- initialization via constructor
};

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by:alcindor
ID: 34150966
I have already accepted this solution. There is a fault on your web application ?
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LVL 53

Expert Comment

by:Infinity08
ID: 34152726
It looks like it worked now. If you think there is a bug or other issue with the web site, you can report that by posting a question in the EE bugs zone (or the general Community Support zone).
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