C++ Nested class (Make friend outer member function)?

-2

My code:

class Controller {



private:

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init();

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // why don't work ?

    };



private:

     ControllerMetals * controlMetals;



public:

    void start(ControllerMetals & c);

    ControllerMetals * getControlMetals() const;

    Controller();



};

I want to make a void start to have access private member in ControllerMetals class. Why friend statements don't work ?

asked Nov 22 '18 at 22:11

loczek

1

Since ControllerMetals is private inside of Controller, why not make everything public in ControllerMetals? Obviously the nested private class is tightly coupled with the outer class.
– Eljay
Nov 22 '18 at 22:25

I have a task and I must declare my inner class as private member of outer class. And all member must be private.
– loczek
Nov 22 '18 at 22:56

Controller::start doesn't exist when you friend it. You can declare a datatype when you friend it but I don't think you can with a function. Forward declare ControllerMetals so you can refer to it and then formally define it after the functions. Why the hell didn't I just make an answer?
– user4581301
Nov 23 '18 at 1:48

add a comment |

-2

My code:

class Controller {



private:

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init();

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // why don't work ?

    };



private:

     ControllerMetals * controlMetals;



public:

    void start(ControllerMetals & c);

    ControllerMetals * getControlMetals() const;

    Controller();



};

I want to make a void start to have access private member in ControllerMetals class. Why friend statements don't work ?

asked Nov 22 '18 at 22:11

loczek

1

Since ControllerMetals is private inside of Controller, why not make everything public in ControllerMetals? Obviously the nested private class is tightly coupled with the outer class.
– Eljay
Nov 22 '18 at 22:25

I have a task and I must declare my inner class as private member of outer class. And all member must be private.
– loczek
Nov 22 '18 at 22:56

Controller::start doesn't exist when you friend it. You can declare a datatype when you friend it but I don't think you can with a function. Forward declare ControllerMetals so you can refer to it and then formally define it after the functions. Why the hell didn't I just make an answer?
– user4581301
Nov 23 '18 at 1:48

add a comment |

-2

My code:

class Controller {



private:

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init();

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // why don't work ?

    };



private:

     ControllerMetals * controlMetals;



public:

    void start(ControllerMetals & c);

    ControllerMetals * getControlMetals() const;

    Controller();



};

I want to make a void start to have access private member in ControllerMetals class. Why friend statements don't work ?

asked Nov 22 '18 at 22:11

loczek

My code:

class Controller {



private:

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init();

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // why don't work ?

    };



private:

     ControllerMetals * controlMetals;



public:

    void start(ControllerMetals & c);

    ControllerMetals * getControlMetals() const;

    Controller();



};

I want to make a void start to have access private member in ControllerMetals class. Why friend statements don't work ?

c++ class nested friend

asked Nov 22 '18 at 22:11

loczek

asked Nov 22 '18 at 22:11

loczek

asked Nov 22 '18 at 22:11

loczek

asked Nov 22 '18 at 22:11

loczek

asked Nov 22 '18 at 22:11

loczek

1

Since ControllerMetals is private inside of Controller, why not make everything public in ControllerMetals? Obviously the nested private class is tightly coupled with the outer class.
– Eljay
Nov 22 '18 at 22:25

I have a task and I must declare my inner class as private member of outer class. And all member must be private.
– loczek
Nov 22 '18 at 22:56

Controller::start doesn't exist when you friend it. You can declare a datatype when you friend it but I don't think you can with a function. Forward declare ControllerMetals so you can refer to it and then formally define it after the functions. Why the hell didn't I just make an answer?
– user4581301
Nov 23 '18 at 1:48

add a comment |

1

Since ControllerMetals is private inside of Controller, why not make everything public in ControllerMetals? Obviously the nested private class is tightly coupled with the outer class.
– Eljay
Nov 22 '18 at 22:25

I have a task and I must declare my inner class as private member of outer class. And all member must be private.
– loczek
Nov 22 '18 at 22:56

Controller::start doesn't exist when you friend it. You can declare a datatype when you friend it but I don't think you can with a function. Forward declare ControllerMetals so you can refer to it and then formally define it after the functions. Why the hell didn't I just make an answer?
– user4581301
Nov 23 '18 at 1:48

Since ControllerMetals is private inside of Controller, why not make everything public in ControllerMetals? Obviously the nested private class is tightly coupled with the outer class.
– Eljay
Nov 22 '18 at 22:25

I have a task and I must declare my inner class as private member of outer class. And all member must be private.
– loczek
Nov 22 '18 at 22:56

Controller::start doesn't exist when you friend it. You can declare a datatype when you friend it but I don't think you can with a function. Forward declare ControllerMetals so you can refer to it and then formally define it after the functions. Why the hell didn't I just make an answer?
– user4581301
Nov 23 '18 at 1:48

add a comment |

1 Answer
1

active

oldest

votes

Problem

Member functions have to be declared before you can friend them. friend has a built-in forward declaration for a data type, but not for members of that data type.

Solution

Personally I agree with Eljay's comment, make everything in ControllerMetals public because it is already hidden by Controller, but if the assignment says no, do what you have to do to pass the course.

Simple solution:

You friend the whole Controller class to get the members, but this might be too broad.

More complicated, tighter-grained solution:

More stuff around so that the required member function is declared before ControllerMetals. You can get away with this because the start only needs a declaration of ControllerMetals in order to take references to it.

class Controller {



    class ControllerMetals; // forward declare to make available for referencing

public:

    void start(ControllerMetals & c); // start now known. Can friend

    ControllerMetals * getControlMetals() const;

    Controller();



private:

    // now we can fully define ControllerMetals

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init(); // why is this not done in the constructor?

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // now works

    };

     ControllerMetals * controlMetals;





};

edited Nov 23 '18 at 15:30

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

add a comment |

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1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

Problem

Member functions have to be declared before you can friend them. friend has a built-in forward declaration for a data type, but not for members of that data type.

Solution

Simple solution:

You friend the whole Controller class to get the members, but this might be too broad.

More complicated, tighter-grained solution:

class Controller {



    class ControllerMetals; // forward declare to make available for referencing

public:

    void start(ControllerMetals & c); // start now known. Can friend

    ControllerMetals * getControlMetals() const;

    Controller();



private:

    // now we can fully define ControllerMetals

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init(); // why is this not done in the constructor?

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // now works

    };

     ControllerMetals * controlMetals;





};

edited Nov 23 '18 at 15:30

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

add a comment |

Problem

Member functions have to be declared before you can friend them. friend has a built-in forward declaration for a data type, but not for members of that data type.

Solution

Simple solution:

You friend the whole Controller class to get the members, but this might be too broad.

More complicated, tighter-grained solution:

class Controller {



    class ControllerMetals; // forward declare to make available for referencing

public:

    void start(ControllerMetals & c); // start now known. Can friend

    ControllerMetals * getControlMetals() const;

    Controller();



private:

    // now we can fully define ControllerMetals

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init(); // why is this not done in the constructor?

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // now works

    };

     ControllerMetals * controlMetals;





};

edited Nov 23 '18 at 15:30

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

add a comment |

Problem

Member functions have to be declared before you can friend them. friend has a built-in forward declaration for a data type, but not for members of that data type.

Solution

Simple solution:

You friend the whole Controller class to get the members, but this might be too broad.

More complicated, tighter-grained solution:

class Controller {



    class ControllerMetals; // forward declare to make available for referencing

public:

    void start(ControllerMetals & c); // start now known. Can friend

    ControllerMetals * getControlMetals() const;

    Controller();



private:

    // now we can fully define ControllerMetals

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init(); // why is this not done in the constructor?

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // now works

    };

     ControllerMetals * controlMetals;





};

edited Nov 23 '18 at 15:30

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

Problem

Member functions have to be declared before you can friend them. friend has a built-in forward declaration for a data type, but not for members of that data type.

Solution

Simple solution:

You friend the whole Controller class to get the members, but this might be too broad.

More complicated, tighter-grained solution:

class Controller {



    class ControllerMetals; // forward declare to make available for referencing

public:

    void start(ControllerMetals & c); // start now known. Can friend

    ControllerMetals * getControlMetals() const;

    Controller();



private:

    // now we can fully define ControllerMetals

    class ControllerMetals {

        private:

            int m_size;

            Metals * m_metals;

        public:

            ControllerMetals();

            Metals & getMetals() const;

            int getSize() const;

            void setSize(int size) { m_size = size; }

            void init(); // why is this not done in the constructor?

            void show();

            void erase();

        friend void Controller::start(ControllerMetals & c); // now works

    };

     ControllerMetals * controlMetals;





};

edited Nov 23 '18 at 15:30

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

edited Nov 23 '18 at 15:30

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

answered Nov 23 '18 at 1:53

user4581301

19.5k51831

add a comment |

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