overloading a member inside another member - c++

Question

in my school assignment i need a small help
this is my header file:
#include <iostream>
#include <cstring>
using namespace std;
#include "ISBNPrefix.h"
class ISBN
{
char str[11];
char area[6];
char publisher[8];
char title[7];
bool registered;
public:
ISBN();
ISBN(const char*,ISBNPrefix &);
void toStr(char*)const;
void toStrWithStyle(char*)const;
bool empty()const;
bool isRegistered() const;
bool read(istream& is, const ISBNPrefix& list);
void display(ostream&) const;
};
int isValid(const char* str);
and this is the implementation of my file:
#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include <iomanip>
using namespace std;
#include "ISBN.h"
ISBN::ISBN()
{
str[0]='\0';
area[0]='\0';
publisher[0]='\0';
title[0]='\0';
registered=false;
}
ISBN::ISBN(const char* s,ISBNPrefix& p)
{
if(isValid(s)==1)
{
strcpy_s(str,s);
}
else
{
*this=ISBN();
}
}
bool ISBN::empty()const
{
bool chk=false;
if(str[0]=='\0')
chk=true;
return chk;
}
void ISBN::toStrWithStyle(char* s) const
{
if(registered)
{
sprintf(s,"%s-%s-%s-%c",area,publisher,title,str[9]);
}
else
{
toStr(s);
}
}
void ISBN::toStr(char* s) const
{
if (str[0]!='\0')
strcpy(s,str);
else
strcpy(s,"no data");
}
void ISBN::display(ostream & os) const
{
char str[14];
toStrWithStyle(str);
cout<< setw (13) <<str;
}
int isValid(const char* str)
{
int rc=0;
if(str!=0)
{
int sum,i=0;
sum=0;
for(i=0;i<10;i++)
sum+=(str[i]-'0')*(10-i);
if(sum%11==0)
{
rc= 1;
}
}
else
rc=0;
return rc;
}
bool ISBN::read(istream& is, const ISBNPrefix& list)
{
char str[11];
bool quit=false;
bool ok=false;
char lists;
do{
cout<<"ISBN (0 to quit) : ";
is.getline(str,11); //or is.get(str,11)
if(strcmp(str,"0")==0)
quit=true;
else if (isValid(str)==1)
{
*this=ISBN(str,list);
ok=true;
cout<<"isbn is valid"<<endl;
}
else
{
*this=ISBN();
cout<<"invalid ISBN"<<endl;
}
} while(!quit&&!ok);
return !quit;
}
in the ISBN::read where I say
*this=ISBN(str,list);
i want to overload another member but i can't.
can anyone tell me how can i do that?

Answer 1

First I would suggest use std::string in favour of char[]. It will save a lot of trouble. For reading ISBN I would write something like this:
bool ISBN::read(istream& is)
{
ISBN result;
// reading into result
std::swap(*this,result);
return !quit;
}
Or even better (as a non member function):
std::istream& operator>>(istream& is, ISBN& obj)
{
ISBN result;
// reading into result
is(!quit)
is.clear(std::ios_base::failbit);
std::swap(obj,result);
return is;
}
In any way you should RAII classes for your resources. In your special case std::string instead of char[].