NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/13169

Text File | 1996-08-05 | 5.4 KB | 178 lines

Path: news.compuserve.com!newsmaster
From: Philippe Verdy <[e-mail]>
Newsgroups: comp.lang.c,comp.lang.c++
Subject: Re: Linker error problem
Date: 23 Mar 1996 23:18:39 GMT
Organization: CompuServe Incorporated
Message-ID: <4j20sf$[e-mail]>
NNTP-Posting-Host: ad53-232.compuserve.com

[e-mail] (Gregary J Boyles) s'Θcrit :
> I am getting a linker error as follows. Undefined symbol
> Address::ThisPtrList in module address.cpp.
> I don't understand this non sense because it is defined
> as a static class member and its value is initialized.
> See $$$$ for definitions #### for causes of the error (if
> I comment out these lines then the error disappears.
>
> // address.h
> #include <iostream.h>
>
> #ifndef __ADDRESS_H
> #define __ADDRESS_H
> #define SIZE 100
>
> #include "defines.h"
>
> class Address
> {
>      private : int Number;
>            char *Street;
>            char *City;
>            int Zip;
>         $$$$$$   static Address *ThisPtrList[SIZE];
-------------------------------------------------------
Here you declare: Address * Address::ThisPtrList[SIZE]
-------------------------------------------------------
>            static unsigned int NumberInstances;
>            static unsigned int InstanceNumber;
>
>      public : // Constructors
>           Address(int ANumber,const char *AStreet,const char *ACity,int Zip);
>           Address();
>           // Copy constructor
>           Address(Address& AnAddress);
>           // Deconstructor
>           ~Address();
>           // Operator overloads
>           friend ostream& operator << (ostream& OutPutStream,Address& AnAddress);
>           friend istream& operator >>(istream& InPutStream,Address& AnAddress);
>           // Functions
>           void Change(int ANumber,const char *AStreet,const char *ACity,int AZip);
>           unsigned int Address::NumberOfInstances();
>           void Address::DisplayAll();
> };
>
> #endif
>
>
>
> // address.cpp
>
> #include "address.h"
> #include <string.h>
> #include <iostream.h>
>
> // Data initializations
> unsigned int Address::NumberInstances=0;
>
> unsigned int Address::InstanceNumber=0;
>
> $$$$ Address Address::*ThisPtrList={0};
---------------------------------------------------
The previous line is not correct. You only declare
a pointer to a member of the class Address, which points
to an object of type Address. This is valid even if there
is no such member in the class Address !! (the compiler
makes no assumption on WHICH member the pointer should
point to, but only on the type of that member, so that
dereferencing it thru an instance pointer could lead to
a valid complete member reference.)

You should write:
Address * Address::ThisPtrList[SIZE] = {0};
---------------------------------------------------
>
> // Constructors
> Address::Address(int ANumber,const char *AStreet,const char *ACity,int AZip)
> {
>      Number=ANumber;
>      Street=new char[strlen(AStreet)+1];
>      strcpy(Street,AStreet);
>      City=new char[strlen(ACity)+1];
>      strcpy(City,ACity);
>      Zip=AZip;
> ####     ThisPtrList[NumberInstances]=this;
---------------------------------------------------
With the previous correction, this line is correct
---------------------------------------------------
>      NumberInstances++;
>      InstanceNumber=NumberInstances;
> }
>
> Address::Address()
> {
>      Number=0;
>      Street=new char[strlen("")+1];
>      strcpy(Street,"");
>      City=new char[strlen("")+1];
>      strcpy(City,"");
>      Zip=0;
> ####     ThisPtrList[NumberInstances]=this;
---------------------------------------------------
With the previous correction, this line is correct
---------------------------------------------------
>      NumberInstances++;
>      InstanceNumber=NumberInstances;
> }
>
> // Copy constructor
> Address::Address(Address& AnAddress)
> {
>      Number=AnAddress.Number;
>      Street=new char[strlen(AnAddress.Street)+1];
>      strcpy(Street,AnAddress.Street);
>      City=new char[strlen(AnAddress.City)+1];
>      strcpy(City,AnAddress.City);
>      Zip=AnAddress.Zip;
> ####     ThisPtrList[NumberInstances]=this;
---------------------------------------------------
With the previous correction, this line is correct
---------------------------------------------------
>      NumberInstances++;
>      InstanceNumber=NumberInstances;
> }
>
> // Deconstructor
> Address::~Address()
> {
>      Number=0;
>      delete Street;
>      delete City;
>      Zip=0;
> }
>
> // Operator overloads
> ostream& operator <<(ostream& OutPutStream,Address& AnAddress)
> {
>      OutPutStream<<"Street : "<<AnAddress.Number<<" "<<AnAddress.Street<<EOLN;
>      OutPutStream<<"City : "<<AnAddress.City<<EOLN;
>      OutPutStream<<"Zip code : "<<AnAddress.Zip<<EOLN;
>      return(OutPutStream);
> }
>
>
> istream& operator >>(istream& InPutStream,Address& AnAddress)
> {
>      char *StreetName,*CityName,ch;
>
>      StreetName=new char[50];
>      CityName=new char[50];
>      cout<<"Number : ";
>      cin>>AnAddress.Number;
>      GetEndOfLine();
>      cout<<"Street : ";
>      cin.getline(StreetName,49,EOLN);
>      delete AnAddress.Street;
>      AnAddress.Street=new char[strlen(StreetName)+1];
>      strcpy(AnAddress.Street,StreetName);
>      cout<<"City : ";
>      cin.getline(CityName,49,EOLN);
>      delete AnAddress.City;
>      AnAddress.City=new char[strlen(CityName)+1];
>      strcpy(AnAddress.City,CityName);
>      cout<<"City : ";
>      cout<<"Zip code : ";
> }