How to make a function friend to both base and derived class Post: 302146334

Sponsored Content

Top Forums Programming How to make a function friend to both base and derived class Post 302146334 by ennstate on Tuesday 20th of November 2007 03:24:00 AM

11-20-2007

Registered User

How to make a function friend to both base and derived class

Hi,
I have a base class and derived a class from the base class, i want to print & read the data for the object created for the derived class,so i have overloaded both the << and >> operators and also have done the foward declaration.

Below is the code snippet,

Code:

#include <iostream>

class Line; // Forward Declaration for friend

class Point {
 private:
   int x,y;
 public:
   virtual void draw() ;
   friend std::ostream& operator<< ( std::ostream& , const Line&);
   friend std::istream& operator>> ( std::istream& ,  Line&);
};


class Line : public Point {
 private:
  int color;
 public :
   void draw () { std::cout<< "Drawing a Line" << std::endl; }
   friend std::ostream& operator<< ( std::ostream& , const Line&);
   friend std::istream& operator>> ( std::istream& ,  Line&);
};

inline
std::ostream& operator<< ( std::ostream &os , const Line &out ) {
  os<<"Line: [" << out.x << "," << out.y << " ," << out.color << " ]" << std::endl;
  return os;
}

inline
std::istream& operator>> ( std::istream &is , const Line &in ) {
  std::cout<<"Line x , y , color info: " << std::endl;
  is >> in.x >> in.y >> in.color;
  return is;
}

int main(int argc, char *aargv) {
 Line new_line;
 std::cin>>new_line;
 std::cout<<new_line;
 return(0);
}

Am using g++ and on compiling i get the below errors, how to fix this

Code:

g++ friends.cpp
friends.cpp: In function `std::istream& operator>>(std::istream&, const Line&)   ':
friends.cpp:8: error: `int Point::x' is private
friends.cpp:34: error: within this context
friends.cpp:8: error: `int Point::y' is private
friends.cpp:34: error: within this context
friends.cpp:18: error: `int Line::color' is private
friends.cpp:34: error: within this context

Thanks
Nagarajan G

ennstate

View Public Profile for ennstate

Find all posts by ennstate

8 More Discussions You Might Find Interesting

1. HP-UX

How to make a loop base on reading a file?

Need help on making a loop script base on what is inside a file... File to read: List.txt List.txt contains below w/c are file name as well: SAMPLEa SAMPLEb SAMPLEc SAMPLEd SAMPLEe SAMPLEf . . . Want to make a loop that will manipulate those that are inside the file.txt w/c are...

2. Programming

Please help debug this friend class in C++

Please help check an old code: #include <iostream> using namespace std; template <class C> class List { //Linked list of C. template<class U> friend class ListItr; private: class ListEl { public: C val; ListEl* next; ListEl(const C& s, ListEl* n) : val(s) { next = n;} };...

3. Programming

Base class's variables not accessible????

Hi friends, The derived class cannot access the base class's variables in my program. You can have a look at my code, I am actually using class templates. #include <iostream> using namespace std; template <class T> class Sum { friend void Check(Sum &s, T a, T b) { T x,...

4. Programming

C++ compilation error when I use predicate friend function in the std::sort()

Hi, Can anyone tell me why the following program is giving compiler error when I use a friend function of a class as the comparison predicate for the third parameter of std::sort() algorithm? How to correct it, keep the 'friend' intact? #include <iostream> #include <vector> #include <list>...

5. Programming

Size of Derived class, upon virtual base class inheritance

I have the two class definition as follows. class A { public: int a; }; class B : virtual public A{ }; The size of class A is shown as 4, and size of class B is shown as 16. Why is this effect ?.

6. Programming

Size of derived class, in case of multiple inheritance

Why, here the size of class 'Derived' is 8 ? class Base1 { public: virtual void f() { } }; class Base2 { public: virtual void f() { } }; class Derived : public Base1, Base2 { public: virtual void f() { } };

7. Programming

C++ : Base class member function not accessible from derived class

Hello All, I am a learner in C++. I was testing my inheritance knowledge with following piece of code. #include <iostream> using namespace std; class base { public : void display() { cout << "In base display()" << endl; } void display(int k) {...

8. Shell Programming and Scripting

Derived both lines base on pattern

Dear All, I have a requests to retrieve all lines if second line last columns meets certain criteria. Here is the output of the result Table: DSSBDW.DA_MASK_CLK_AR 120908 0 86 86 - 1934528 0 70 100 -*- Table: DSSBDW.DA_MASK_CLK_IP 310657 22030 143 185 - 5281169 7 88 77 *-* Table:...

LEARN ABOUT SUSE

iostream

FBB::IOStream(3bobcat)                                     std::istream and std::ostream                                    FBB::IOStream(3bobcat)

NAME

       FBB::IOStream - Combines std::istream and std::ostream features

SYNOPSIS

       #include <bobcat/iostream>
       Linking option: -lbobcat

DESCRIPTION

       This  class combines the features of the std::istream and std::ostream classes. The std::istream and std::ostream may be physically differ-
       ent streams. FBB:IOStream objects may, e.g., be associated with streams wrapped around  pipes  (see,  e.g.,  FBB::IfdStream  and  FBB::OFd-
       Stream), to construct bi-directional pipes.

NAMESPACE

       FBB
       All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

INHERITS FROM

       FBB::IOStreambuf (private inheritance),
       std::istream,
       std::ostream

CONSTRUCTORS

       o      IOStream():
              The  default  constructor  constructs  an  empty FBB::IOStream objects. It should not be used before its open member (see below) was
              called.

       o      IOStream(std::istream &in, std::ostream &out):
              This constructor associates the IOStream object with a std::istream and a std::ostream. All output operations will be passed  on  to
              the  std::ostream, all input operations to the std::istream. The streams passed to IOStream should outlive the IOStream object. This
              constructor performs the actions of the default constructor and then calls the IOStream::open member De copy constructor  is  avail-
              able as well.

MEMBER FUNCTIONS

       All  members  of  std::istream  and  std::ostream  are available, as FBB::IOStream inherits from these classes. Furthermore, when switching
       between std::istream and std::ostream operations, no intermediate seekg() or seekp() operation will normally be required,  since  the  base
       classes will normally be associated with physically different streams.

       o      void open(std::istream &in, std::ostream &out):
              This  member  (re)associates  the IOStream object with a std::istream and a std::ostream. All output operations will be passed on to
              the std::ostream, all input operations to the std::istream. The streams passed to IOStream() should outlive the IOStream object.  If
              this  member  is  called  for an IOStream object already associated with an std::ostream object, the already associated std::ostream
              object is flushed before setting up the new association.

       o      void clear():
              This member clears the error states of the associated std::istream and std::ostream objects.

EXAMPLE

       See the example provided with process(3bobcat).

FILES

       bobcat/iostream - defines the class interface

SEE ALSO

       bobcat(7), ifdstream(3bobcat), iostreambuf(3bobcat), ofdstream(3bobcat), process(3bobcat)

BUGS

       None Reported.

DISTRIBUTION FILES

       o      bobcat_3.01.00-x.dsc: detached signature;

       o      bobcat_3.01.00-x.tar.gz: source archive;

       o      bobcat_3.01.00-x_i386.changes: change log;

       o      libbobcat1_3.01.00-x_*.deb: debian package holding the libraries;

       o      libbobcat1-dev_3.01.00-x_*.deb: debian package holding the libraries, headers and manual pages;

       o      http://sourceforge.net/projects/bobcat: public archive location;

BOBCAT

       Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.

COPYRIGHT

       This is free software, distributed under the terms of the GNU General Public License (GPL).

AUTHOR

       Frank B. Brokken (f.b.brokken@rug.nl).

libbobcat1-dev_3.01.00-x.tar.gz                                      2005-2012                                              FBB::IOStream(3bobcat)