From: "A. Jans-Beken" <jansb000 AT wxs DOT nl>
Newsgroups: comp.os.msdos.djgpp
Subject: C++ array problem
Date: Sun, 13 Dec 1998 22:41:11 +0100
Organization: World Access
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I was experimenting with a template class for arrays. This is an example
in the C++ primer from stanly B. Lippman 2nd edition 1991.

During compiling (or actually I believe its linking) I get this error
message (in a rhide status screen):
---
 Creating: array.exe
 Error: arrmain.o: In function `main':
 arrmain.cpp(4) Error: undefined reference to `ARRAY<int>::init(int
const *, int)'
 arrmain.cpp(7) Error: undefined reference to
`__ls__H1Zi_R7ostreamRt5ARRAY1ZX01_R7ostream'
 There were some errors
---

The init function IS defined. I can't figure out why its complaining
about this. The second error, well I can't cook soup from it.

Someone knows what is happening here? Are there some examples of
variable sized one and two dimensional arrays out there?
Please respond (also) via e-mail...

Complete code follows:
---vvv---array.hpp
//
// array.hpp
// =========
//

#ifndef ARRAY_HPP
#define ARRAY_HPP

template <class Type> class ARRAY;
template <class Type> ostream& operator<<(ostream&, ARRAY<Type>&);

const int DEF_ARRAY_SIZE = 10;

template <class Type>
class ARRAY {

 private:
   int  size;
   Type *ia;

//   void swap(const int, const int);
   void init(const Type *, int);

 public:
   // Constructors ...
   ARRAY(int asize = DEF_ARRAY_SIZE) { init(NULL, asize); }
   ARRAY(const Type *ar, int asize) { init(ar,asize); }
   ARRAY(const ARRAY& src_array) { init(src_array.ia, src_array.size); }

   // Destructor ...
   ~ARRAY() { delete [] ia; }

   // Operators
#ifndef NDEBUG
   // friend ostream& operator<<(ostream&, ARRAY<Type>&);
#endif
   ARRAY& operator=(const ARRAY&);
   Type& operator[](const int ix) { return ia[ix]; }

   // Members & Methods
#ifndef NDEBUG
   void print(ostream&);
#endif
   int get_size() { return size; }
   void grow();
   };
#endif

---vvv---array.cpp
//
// array.cpp
// =========
//

#ifndef NDEBUG
#include <iostream.h>
#endif

#include <assert.h>
#include "array.hpp"

// Operators ...

#ifndef NDEBUG
template <class Type>
ostream& operator<<(ostream& os, ARRAY<Type>& a) {
   a.print(os);
   return os;
   }
#endif

template <class Type>
ARRAY<Type>& ARRAY<Type>::operator=(const ARRAY& src_array) {
   if (this == &src_array) return *this;

   delete [] ia;
   init(src_array.ia, src_array.size);
   return *this;
   }

// Members ...
#ifndef NDEBUG
template <class Type>
void ARRAY<Type>::print(ostream& os) {
   // Address of array...
   // os << "($" << hex << &t << dec << ") ";
   os << "Array $" << size << "\n";
   // << hex << *a << dec << ": ";

   // Values of array-values...
//   for (int i = 0; i < a.size; i++) {
//      os << a.ia[i] << " ";
   }
#endif

template <class Type>
void ARRAY<Type>::init(const Type *src_array, int n) {
   ia = new Type[size = n];
   assert(ia != NULL);

   for (int i = 0; i < size; i++)
      ia[i] = (src_array != NULL) ? src_array[i] : (Type) 0;
   }

template <class Type>
void ARRAY<Type>::grow() {
   Type *old_array = ia;
   int old_size = size;

   int new_size = old_size + (old_size/2) + 1;
   ia = new Type[size = new_size];
   assert(ia != NULL);

//   for (int i = 0; i < old_size; i++)
//      ia[i] = old_array[i];
//   for ( ; i < size; i++)
//      ia[i] = (Type) 0;
   for (int i = 0; i < size; i++)
      ia[i] = (i < old_size) ? old_array[i] : (Type) 0;
   }

---vvv---arrmain.cpp
/*
 * arrmain.cpp
 */

#include <iostream.h>
#include <conio.h>
#include <assert.h>
#include "array.hpp"

int main () {
   MSS_LOG_MSG("Starting a LOG session");

   cout << "Testing the array class\n";
   cout << "-----------------------\n";

   ARRAY<int> arint;
   cout << arint << "\n";

   getch();
   return 0;
   }

---