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Private or Public?

This is a discussion on Private or Public? within the C++ Programming forums, part of the General Programming Boards category; Hi, I have a class of some objects. The class is Code: #ifndef SALES_DATA_H_INCLUDED #define SALES_DATA_H_INCLUDED #include <string> #include <iostream> ...

  1. #1
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    Private or Public?

    Hi, I have a class of some objects. The class is
    Code:
    #ifndef SALES_DATA_H_INCLUDED
    #define SALES_DATA_H_INCLUDED
    #include <string>
    #include <iostream>
    using namespace std;
    class Sales_data{
    friend ostream &print(ostream&,const Sales_data&);
    friend istream &read(istream&,Sales_data&);
    public:
        Sales_data &combine(const Sales_data&);
        Sales_data()=default;
        Sales_data(istream &is)
         {
             double price = 0;
             is >> (*this).bookNo >> (*this).units_sold >> price;
             (*this).revenue = price * (*this).units_sold;
         };
    
        string isbn() const {return bookNo;}
        double avg_price() const {return units_sold?revenue/units_sold:0;}
    private:
        std::string bookNo;
        unsigned units_sold;
        double revenue;
    };
    
    
    Sales_data add(const Sales_data &lhs,const Sales_data &rhs)
    {
        Sales_data sum=lhs;
        sum.combine(rhs);
        return sum;
    }
    ostream &print(ostream &os,const Sales_data &item)
    {
        os<<item.isbn()<<" was sold "<<item.units_sold<<" copies at total tk "<<item.revenue
        <<" and the average price is "<<item.avg_price()<<endl;
        return os;
    }
    //input function
    istream &read(istream &is, Sales_data &item)
    {
    double price = 0;
    is >> item.bookNo >> item.units_sold >> price;
    item.revenue = price * item.units_sold;
    return is;
    }
    Sales_data& Sales_data::combine(const Sales_data &rhs)
    {
      units_sold+=rhs.units_sold;
      revenue+=rhs.revenue;
      return *this;
    }
    
    #endif // SALES_DATA_H_INCLUDED
    But, This doesnt compile and gives error at line 27. Says, objects are private with respect to that context. but there is nothing there..

  2. #2
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    Other than the missing main() this compiles without errors for me.

    Jim

  3. #3
    C++まいる!Cをこわせ! Elysia's Avatar
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    Is this a header? Then, don't use "using namespace." It's considered bad practice.
    Other than that, you really should be consistent with indentation, remove the "(*this)." parts, and read this: SourceForge.net: Do not remove parameter names - cpwiki
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  4. #4
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    My main source file is
    Code:
    #include <iostream>
    #include <string>
    using namespace std;
    #include "Sales_data.h"
    #include "funtions.h"
    int main()
    {
    Sales_data total(cin);
    Sales_data sum=total,trans;
    while(read(cin,trans))
    {
    
    
        if(trans.isbn()==total.isbn())
        {
            total.combine(trans);
            sum.combine(trans);
    
        }
        else
        {
            print(cout,total);
            sum.combine(trans);
            total=trans;
        }
    }
    print(cout,total);
    cout<<"total  "<<sum.units_sold<<" books sold in  "<<sum.revenue<<" dollar"<<endl;
    cout<<"average sales price of all book is "<<sum.avg_price()<<" dollar"<<endl;
    
    
    }
    and I have also modified the header.. still dont compile
    Code:
    #ifndef SALES_DATA_H_INCLUDED
    #define SALES_DATA_H_INCLUDED
    
    
    class Sales_data{
    friend ostream &print(ostream&,const Sales_data&);
    friend istream &read(istream&,Sales_data&);
    public:
        Sales_data &combine(const Sales_data&);
        Sales_data()=default;
        Sales_data(istream &is)
         {
             double price = 0;
             is >> (*this).bookNo >> (*this).units_sold >> price;
             (*this).revenue = price * (*this).units_sold;
         };
    
        string isbn() const {return bookNo;}
        double avg_price() const {return units_sold?revenue/units_sold:0;}
    private:
        std::string bookNo;
        unsigned units_sold;
        double revenue;
    };
    
    Sales_data add(const Sales_data&,const Sales_data&);
    ostream &print(ostream&,const Sales_data&);
    istream &read(istream&,Sales_data&);
    
    #endif // SALES_DATA_H_INCLUDED
    and heres the header of my functions
    Code:
    #ifndef FUNTIONS_H_INCLUDED
    #define FUNTIONS_H_INCLUDED
    Sales_data add(const Sales_data &lhs,const Sales_data &rhs)
    {
        Sales_data sum=lhs;
        sum.combine(rhs);
        return sum;
    }
    ostream &print(ostream &os,const Sales_data &item)
    {
        os<<item.isbn()<<" was sold "<<item.units_sold<<" copies at total tk "<<item.revenue
        <<" and the average price is "<<item.avg_price()<<endl;
        return os;
    }
    //input function
    istream &read(istream &is, Sales_data &item)
    {
       double price = 0;
       is >> item.bookNo >> item.units_sold >> price;
       item.revenue = price * item.units_sold;
       return is;
    }
    Sales_data& Sales_data::combine(const Sales_data &rhs)
    {
      units_sold+=rhs.units_sold;
      revenue+=rhs.revenue;
      return *this;
    }
    
    #endif // FUNTIONS_H_INCLUDED

  5. #5
    C++ Witch laserlight's Avatar
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    Don't do this:
    Code:
    using namespace std;
    #include "Sales_data.h"
    #include "funtions.h"
    using directives should not come before header inclusions like that. Neither should they be at file scope in the header files. Rather, fully qualify those names.

    Now, what is the error message(s)?
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  6. #6
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    Found the error, I was Using
    Code:
    cout<<"total  "<<sum.units_sold<<" books sold in  "<<sum.revenue<<" dollar"<<endl;
    cout<<"average sales price of all book is "<<sum.avg_price()<<" dollar"<<endl;
    in main function though it was private.
    using directives should not come before header inclusions like that. Neither should they be at file scope in the header files. Rather, fully qualify those names.
    Are you suggesting I write the code like this
    Code:
    std::string bookno;
    std::cout<<"bla bla";
    std::ostream()
    like this?? but that takes a lot more extra writings..of the same word 'std' whats the problem in using directives?

  7. #7
    C++ Witch laserlight's Avatar
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    No, my comments are with respect to your header files at file scope. If you want to have a using directive in a source file after header inclusions, or in a header but within a function scope, go ahead. Just note that indiscriminate use of using directives and using declarations can lead to name collision, possibly causing a compile error or perhaps changing the meaning of your code to something that you did not expect.
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  8. #8
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    Thanks for the advise.. I will be carefull next time..

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