NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/9050

Text File | 1996-08-05 | 6.6 KB | 280 lines

Newsgroups: comp.lang.c++
Path: tday.slip.netcom.com!user
From: [e-mail] (Tony Day)
Subject: Help with bizzare bug (Long)
Message-ID: <[e-mail]>
Sender: [e-mail]
Nntp-Posting-Host: tday.slip.netcom.com
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
Date: Wed, 28 Feb 1996 05:56:13 GMT

I am working through the Prata book to teach myself C++ and I have come
across a bizzarre bug in my atempt to do one of the problems.  The
conseuence of the bug is that after a certain line of code, "\n" is
treated as the string "Smiley"!! (Using Symantec 7.0 Mac)

The offending function is an overloaded assignment operator:

>NameAr & NameAr::operator=(const NameAr & a)
>{
>    if (this == &a)      // if object assigned to self,
>      return *this;  // don't change anything
>   ArrayDb::operator=(a);
>   delete [] name;
>   name = new char[strlen(a.name)+1];
>   strcpy(name, a.name);
>   return *this;
>}

and the offending statement is "delete [] name" (if it is removed the
program runs as wriiten)

I suspect that this is one delete too many, but cannot see why.  If anyone
else can, please let me know.  Complete code follows.

Thanks v.very much

Tony


HEADER FILE FOR BASE AND DERIVED CLASS

// arraydb.h -- define array class
#ifndef _ARRAYDB_H_
#define _ARRAYDB_H_
#include <iostream.h>
#include <string.h>

class ArrayDb
{
private:
   unsigned int size;         // number of array elements
protected:
   double * arr;                       // address of first element
public:
   ArrayDb();                          // default constructor
   // create an ArrayDb of n elements, set each to val
   ArrayDb(unsigned int n, double val = 0.0);
   // create an ArrayDb of n elements, initialize to array pn
   ArrayDb(const double * pn, unsigned int n);
   ArrayDb(const ArrayDb & a);         // copy constructor
   virtual ~ArrayDb();                         // destructor
   unsigned int arsize() const {return size;}   // returns array size
// overloaded operators
   virtual double & operator[](int i);       // array indexing
   virtual const double & operator[](int i) const; // array indexing (no =)
   virtual ArrayDb & operator=(const ArrayDb & a);
   friend ostream & operator<<(ostream & os, const ArrayDb & a);
};

class NameAr: public ArrayDb
{
protected:
   char * name;
public:
   NameAr();                         // default constructor
   // create an ArrayDb of n elements, set each to val
   NameAr(unsigned int n, double val = 0.0, char * n = "Smiley");
   // create an ArrayDb of n elements, initialize to array pn
   NameAr(const double * pn, unsigned int n, char * n = "Smiley");
   NameAr(const ArrayDb & a);
   NameAr(const NameAr & a);         // copy constructor
   ~NameAr();                         // destructor
   NameAr & operator=(const NameAr & a);
   void setname(const char* a);
   friend ostream & operator<<(ostream & os, const NameAr & a);
};

#endif

CLASS METHODS FOR BASE AND DERIVED CLASS

 arraydb.cpp -- ArrayDb class methods
#include <iostream.h>
#include <stdlib.h>   // exit() prototype
#include "12_2arraydb.h"

// default constructor -- no arguments
ArrayDb::ArrayDb()
{
   arr = NULL;
   size = 0;
}

// constructs array of n elements, each set to val
ArrayDb::ArrayDb(unsigned int n, double val)
{
   arr = new double[n];
   size = n;
   for (int i = 0; i < size; i++)
       arr[i] = val;
}

// initialize ArrayDb object to a non-class array
ArrayDb::ArrayDb(const double *pn, unsigned int n)
{
   arr = new double[n];
   size = n;
   for (int i = 0; i < size; i++)
       arr[i] = pn[i];
}

// initialize ArrayDb object to another ArrayDb object
ArrayDb::ArrayDb(const ArrayDb & a)
{
   size = a.size;
   arr = new double[size];
   for (int i = 0; i < size; i++)
       arr[i] = a.arr[i];
}

ArrayDb::~ArrayDb()
{
   delete [] arr;
}

// let user access elements by index (assignment allowed)
double & ArrayDb::operator[](int i)
{
   // check index before continuing
   if (i < 0 || i >= size)
   {
      cerr << "Error in array limits: "
         << i << " is a bad index\n";
      exit(1);
   }
   return arr[i];
}

// let user access elements by index (assignment disallowed)
const double & ArrayDb::operator[](int i) const
{
   // check index before continuing
   if (i < 0 || i >= size)
   {
      cerr << "Error in array limits: "
         << i << " is a bad index\n";
      exit(1);
   }
   return arr[i];
}

// define class assignment
ArrayDb & ArrayDb::operator=(const ArrayDb & a)
{
   if (this == &a)      // if object assigned to self,
      return *this;  // don't change anything
   delete arr;
   size = a.size;
   arr = new double[size];
   for (int i = 0; i < size; i++)
       arr[i] = a.arr[i];
   return *this;
}

// quick output, 5 values to a line
ostream & operator<<(ostream & os, const ArrayDb & a)
{
   for (int i = 0; i < a.size; i++)
   {
       os << a.arr[i] << " ";
       if (i % 5 == 4)
           os << "\n";
   }
   if (i % 5 != 0)
       os << "\n";
   return os;
}


NameAr::NameAr()
{
   name = new char[strlen("Smiley")+1];
   name = "Smiley";
}

NameAr::NameAr(unsigned int n, double val, char * m): ArrayDb(n, val)
{
   name = new char[strlen(m)+1];
   strcpy(name,m);
}

NameAr::NameAr(const double * pn, unsigned int n, char * m ): ArrayDb(pn, n)
{
   name = new char[strlen(m)+1];
   strcpy(name,m);
}

NameAr::NameAr(const ArrayDb & a): ArrayDb(a)
{
   name = new char[strlen("Smiley")+1];
   name = "Smiley";
}

NameAr::NameAr(const NameAr & a)
{
   ArrayDb::ArrayDb(a);
   name = new char[strlen(a.name)+1];
   strcpy(name,a.name);
}

NameAr::~NameAr()
{
   delete [] name;
}

NameAr & NameAr::operator=(const NameAr & a)
{
    if (this == &a)      // if object assigned to self,
      return *this;  // don't change anything
   ArrayDb::operator=(a);

   delete [] name;

   name = new char[strlen(a.name)+1];

   strcpy(name, a.name);
   return *this;
}

void NameAr::setname(const char* a)
{
   delete [] name;
   name = new char[strlen(a)+1];
   strcpy(name, a);
}

ostream & operator<<(ostream & os, const NameAr & a)
{
   os << ArrayDb(a);
   os << a.name;
   os << "\n";
   return os;
}

MAIN PROGRAM

//ouze12_2main.cpp for 12.2

#include <iostream.h>
#include "12_2arraydb.h"
const int SZ = 5;
int main(void)
{
   double it[SZ] = {19.0, 20.0, 18.0, 16.0, 18.5};
   ArrayDb ita(it, SZ);
   cout << "Displaying an ArrayDb object:\n";
   cout << ita;
   NameAr itna(ita);  //default name
   cout << "Displaying a NameAr object:\n";
   cout << itna;
   NameAr aldo(2 * SZ, 13.2, "Aldo");
   for (int i = 0; i<2*SZ; i++)  // check []
      aldo[i] = aldo[i] + i/2.0;
   cout << aldo;
   itna = aldo; //check assignment
   cout << itna;

      return 0;
}