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I have two classes; Salary that is intended to hold information and calculations regarding the salary of an employee and Employee that has an object of type class Salary and some members like name and address of the employee...

What I want to do is to prevent class Salary from being instantiated and only class Employee can instantiate it. So I declared the constructors of Salary private and made Employee friend of Salary. But I get errors:

class Employee;



class Salary {

    public:



    private:

        Salary() : revenue_{}, cost_{} {}

        Salary(int x, int y) : revenue_{ x },

        cost_{ y } {



        }

        int revenue_, cost_;

        friend class Employee;

};



class Employee {

    public:

        std::string name_;

        Salary sal;

};



int main(){



    Employee emp{}; // "Salary::Salary()" is inaccessible

}

The problem raised for me if I forward declare main:

int main(int, char*[]);

And make main friend of class Salary so in Salary:

class Salary {

    //...

    friend int main(int argc, char* argv[]);

};

Now the program compiles correctly!

*** Another thing in main if I declare an object this way:

Employee emp; // ok

Employee emp{}; // error?

edited 43 mins ago

asked 50 mins ago

Syfu_H

35518

Why are you making Salary's constructor private? It seems like there are contexts when you'd want to use Salary outside of Employee

– J. Antonio Perez
7 mins ago

add a comment |

class Employee;



class Salary {

    public:



    private:

        Salary() : revenue_{}, cost_{} {}

        Salary(int x, int y) : revenue_{ x },

        cost_{ y } {



        }

        int revenue_, cost_;

        friend class Employee;

};



class Employee {

    public:

        std::string name_;

        Salary sal;

};



int main(){



    Employee emp{}; // "Salary::Salary()" is inaccessible

}

The problem raised for me if I forward declare main:

int main(int, char*[]);

And make main friend of class Salary so in Salary:

class Salary {

    //...

    friend int main(int argc, char* argv[]);

};

Now the program compiles correctly!

*** Another thing in main if I declare an object this way:

Employee emp; // ok

Employee emp{}; // error?

edited 43 mins ago

asked 50 mins ago

Syfu_H

35518

Why are you making Salary's constructor private? It seems like there are contexts when you'd want to use Salary outside of Employee

– J. Antonio Perez
7 mins ago

add a comment |

class Employee;



class Salary {

    public:



    private:

        Salary() : revenue_{}, cost_{} {}

        Salary(int x, int y) : revenue_{ x },

        cost_{ y } {



        }

        int revenue_, cost_;

        friend class Employee;

};



class Employee {

    public:

        std::string name_;

        Salary sal;

};



int main(){



    Employee emp{}; // "Salary::Salary()" is inaccessible

}

The problem raised for me if I forward declare main:

int main(int, char*[]);

And make main friend of class Salary so in Salary:

class Salary {

    //...

    friend int main(int argc, char* argv[]);

};

Now the program compiles correctly!

*** Another thing in main if I declare an object this way:

Employee emp; // ok

Employee emp{}; // error?

edited 43 mins ago

asked 50 mins ago

Syfu_H

35518

class Employee;



class Salary {

    public:



    private:

        Salary() : revenue_{}, cost_{} {}

        Salary(int x, int y) : revenue_{ x },

        cost_{ y } {



        }

        int revenue_, cost_;

        friend class Employee;

};



class Employee {

    public:

        std::string name_;

        Salary sal;

};



int main(){



    Employee emp{}; // "Salary::Salary()" is inaccessible

}

The problem raised for me if I forward declare main:

int main(int, char*[]);

And make main friend of class Salary so in Salary:

class Salary {

    //...

    friend int main(int argc, char* argv[]);

};

Now the program compiles correctly!

*** Another thing in main if I declare an object this way:

Employee emp; // ok

Employee emp{}; // error?

c++ constructor friend-class

edited 43 mins ago

asked 50 mins ago

Syfu_H

35518

edited 43 mins ago

asked 50 mins ago

Syfu_H

35518

edited 43 mins ago

asked 50 mins ago

Syfu_H

35518

asked 50 mins ago

Syfu_H

35518

asked 50 mins ago

Syfu_H

35518

Why are you making Salary's constructor private? It seems like there are contexts when you'd want to use Salary outside of Employee

– J. Antonio Perez
7 mins ago

add a comment |

Why are you making Salary's constructor private? It seems like there are contexts when you'd want to use Salary outside of Employee

– J. Antonio Perez
7 mins ago

Why are you making Salary's constructor private? It seems like there are contexts when you'd want to use Salary outside of Employee

– J. Antonio Perez
7 mins ago

add a comment |

4 Answers
4

active

oldest

votes

Because you don't provide a constructor for Employee the braces in your initialization Employee emp{}; will perform an aggregate initialization, which essentially means that each member is initialized one-by-one using the default rules, in the context of main(). Since main() doesn't have access to the Salary constructor, it fails.

As others have pointed out, adding an Employee default constructor will resolve your problem:

class Employee {

    public:

        Employee() = default;

        std::string name_;

        Salary sal;

};

edited 16 mins ago

answered 31 mins ago

zdan

22.1k34864

1

I'm trying on MSVS and only Employee() {}; allows Employee emp{}; to compile. Clang seems to accept Employee() = default;, but then again, Clang seems to accept having no default constructor here.

– wally
14 mins ago

GCC does the same as Clang, and doesn't need a default constructor to compile in this case. Have you tried this answer on any specific compiler?

– wally
3 mins ago

add a comment |

You have to explicitly declare the default constructor of class Employee thus you can initialize an abject via uniform initialization:

class Employee {

    public:

        Employee(){} // add it

        std::string name_;

        Salary sal;

};



int main(){

    Employee emp{}; // now this should compile



}

answered 33 mins ago

Raindrop7

3,74531224

add a comment |

You need Employee's ctor to call the ctor of Salary. The ctor of Salary is not accessible from main.

eg:

class Employee {

public:

    Employee() : sal() {}

    public:

        std::string name_;

        Salary sal;

};

edited 22 mins ago

Pavan Manjunath

20.1k1181108

answered 43 mins ago

schuess

536416

add a comment |

If you erase the "{}" after "Employee emp" in your main() function it compiles just fine (gcc 7.3.1 on Fedora 27).

answered 43 mins ago

Eric Sokolowsky

514

1

I recommend explaining why.

– user4581301
41 mins ago

Yes. Not onyl GCC but also MSVC14 also compiles Employee emp; but why?

– Syfu_H
39 mins ago

@Syfu_H Value Initialization. And I could be mistaken here (been caught on this in the past), but the Value Initialization is being replaced by Aggregate Initialization

– user4581301
31 mins ago

add a comment |

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4 Answers
4

active

oldest

votes

4 Answers
4

active

oldest

votes

As others have pointed out, adding an Employee default constructor will resolve your problem:

class Employee {

    public:

        Employee() = default;

        std::string name_;

        Salary sal;

};

edited 16 mins ago

answered 31 mins ago

zdan

22.1k34864

1

I'm trying on MSVS and only Employee() {}; allows Employee emp{}; to compile. Clang seems to accept Employee() = default;, but then again, Clang seems to accept having no default constructor here.

– wally
14 mins ago

GCC does the same as Clang, and doesn't need a default constructor to compile in this case. Have you tried this answer on any specific compiler?

– wally
3 mins ago

add a comment |

As others have pointed out, adding an Employee default constructor will resolve your problem:

class Employee {

    public:

        Employee() = default;

        std::string name_;

        Salary sal;

};

edited 16 mins ago

answered 31 mins ago

zdan

22.1k34864

1

I'm trying on MSVS and only Employee() {}; allows Employee emp{}; to compile. Clang seems to accept Employee() = default;, but then again, Clang seems to accept having no default constructor here.

– wally
14 mins ago

GCC does the same as Clang, and doesn't need a default constructor to compile in this case. Have you tried this answer on any specific compiler?

– wally
3 mins ago

add a comment |

As others have pointed out, adding an Employee default constructor will resolve your problem:

class Employee {

    public:

        Employee() = default;

        std::string name_;

        Salary sal;

};

edited 16 mins ago

answered 31 mins ago

zdan

22.1k34864

As others have pointed out, adding an Employee default constructor will resolve your problem:

class Employee {

    public:

        Employee() = default;

        std::string name_;

        Salary sal;

};

edited 16 mins ago

answered 31 mins ago

zdan

22.1k34864

edited 16 mins ago

answered 31 mins ago

zdan

22.1k34864

answered 31 mins ago

zdan

22.1k34864

answered 31 mins ago

zdan

22.1k34864

1

I'm trying on MSVS and only Employee() {}; allows Employee emp{}; to compile. Clang seems to accept Employee() = default;, but then again, Clang seems to accept having no default constructor here.

– wally
14 mins ago

GCC does the same as Clang, and doesn't need a default constructor to compile in this case. Have you tried this answer on any specific compiler?

– wally
3 mins ago

add a comment |

1

I'm trying on MSVS and only Employee() {}; allows Employee emp{}; to compile. Clang seems to accept Employee() = default;, but then again, Clang seems to accept having no default constructor here.

– wally
14 mins ago

GCC does the same as Clang, and doesn't need a default constructor to compile in this case. Have you tried this answer on any specific compiler?

– wally
3 mins ago

I'm trying on MSVS and only Employee() {}; allows Employee emp{}; to compile. Clang seems to accept Employee() = default;, but then again, Clang seems to accept having no default constructor here.

– wally
14 mins ago

GCC does the same as Clang, and doesn't need a default constructor to compile in this case. Have you tried this answer on any specific compiler?

– wally
3 mins ago

add a comment |

You have to explicitly declare the default constructor of class Employee thus you can initialize an abject via uniform initialization:

class Employee {

    public:

        Employee(){} // add it

        std::string name_;

        Salary sal;

};



int main(){

    Employee emp{}; // now this should compile



}

answered 33 mins ago

Raindrop7

3,74531224

add a comment |

You have to explicitly declare the default constructor of class Employee thus you can initialize an abject via uniform initialization:

class Employee {

    public:

        Employee(){} // add it

        std::string name_;

        Salary sal;

};



int main(){

    Employee emp{}; // now this should compile



}

answered 33 mins ago

Raindrop7

3,74531224

add a comment |

You have to explicitly declare the default constructor of class Employee thus you can initialize an abject via uniform initialization:

class Employee {

    public:

        Employee(){} // add it

        std::string name_;

        Salary sal;

};



int main(){

    Employee emp{}; // now this should compile



}

answered 33 mins ago

Raindrop7

3,74531224

You have to explicitly declare the default constructor of class Employee thus you can initialize an abject via uniform initialization:

class Employee {

    public:

        Employee(){} // add it

        std::string name_;

        Salary sal;

};



int main(){

    Employee emp{}; // now this should compile



}

answered 33 mins ago

Raindrop7

3,74531224

answered 33 mins ago

Raindrop7

3,74531224

answered 33 mins ago

Raindrop7

3,74531224

answered 33 mins ago

Raindrop7

3,74531224

add a comment |

You need Employee's ctor to call the ctor of Salary. The ctor of Salary is not accessible from main.

eg:

class Employee {

public:

    Employee() : sal() {}

    public:

        std::string name_;

        Salary sal;

};

edited 22 mins ago

Pavan Manjunath

20.1k1181108

answered 43 mins ago

schuess

536416

add a comment |

You need Employee's ctor to call the ctor of Salary. The ctor of Salary is not accessible from main.

eg:

class Employee {

public:

    Employee() : sal() {}

    public:

        std::string name_;

        Salary sal;

};

edited 22 mins ago

Pavan Manjunath

20.1k1181108

answered 43 mins ago

schuess

536416

add a comment |

You need Employee's ctor to call the ctor of Salary. The ctor of Salary is not accessible from main.

eg:

class Employee {

public:

    Employee() : sal() {}

    public:

        std::string name_;

        Salary sal;

};

edited 22 mins ago

Pavan Manjunath

20.1k1181108

answered 43 mins ago

schuess

536416

You need Employee's ctor to call the ctor of Salary. The ctor of Salary is not accessible from main.

eg:

class Employee {

public:

    Employee() : sal() {}

    public:

        std::string name_;

        Salary sal;

};

edited 22 mins ago

Pavan Manjunath

20.1k1181108

answered 43 mins ago

schuess

536416

edited 22 mins ago

Pavan Manjunath

20.1k1181108

edited 22 mins ago

Pavan Manjunath

20.1k1181108

edited 22 mins ago

Pavan Manjunath

20.1k1181108

answered 43 mins ago

schuess

536416

answered 43 mins ago

schuess

536416

answered 43 mins ago

schuess

536416

add a comment |

If you erase the "{}" after "Employee emp" in your main() function it compiles just fine (gcc 7.3.1 on Fedora 27).

answered 43 mins ago

Eric Sokolowsky

514

1

I recommend explaining why.

– user4581301
41 mins ago

Yes. Not onyl GCC but also MSVC14 also compiles Employee emp; but why?

– Syfu_H
39 mins ago

@Syfu_H Value Initialization. And I could be mistaken here (been caught on this in the past), but the Value Initialization is being replaced by Aggregate Initialization

– user4581301
31 mins ago

add a comment |

If you erase the "{}" after "Employee emp" in your main() function it compiles just fine (gcc 7.3.1 on Fedora 27).

answered 43 mins ago

Eric Sokolowsky

514

1

I recommend explaining why.

– user4581301
41 mins ago

Yes. Not onyl GCC but also MSVC14 also compiles Employee emp; but why?

– Syfu_H
39 mins ago

@Syfu_H Value Initialization. And I could be mistaken here (been caught on this in the past), but the Value Initialization is being replaced by Aggregate Initialization

– user4581301
31 mins ago

add a comment |

If you erase the "{}" after "Employee emp" in your main() function it compiles just fine (gcc 7.3.1 on Fedora 27).

answered 43 mins ago

Eric Sokolowsky

514

If you erase the "{}" after "Employee emp" in your main() function it compiles just fine (gcc 7.3.1 on Fedora 27).

answered 43 mins ago

Eric Sokolowsky

514

answered 43 mins ago

Eric Sokolowsky

514

answered 43 mins ago

Eric Sokolowsky

514

answered 43 mins ago

Eric Sokolowsky

514

1

I recommend explaining why.

– user4581301
41 mins ago

Yes. Not onyl GCC but also MSVC14 also compiles Employee emp; but why?

– Syfu_H
39 mins ago

@Syfu_H Value Initialization. And I could be mistaken here (been caught on this in the past), but the Value Initialization is being replaced by Aggregate Initialization

– user4581301
31 mins ago

add a comment |

1

I recommend explaining why.

– user4581301
41 mins ago

Yes. Not onyl GCC but also MSVC14 also compiles Employee emp; but why?

– Syfu_H
39 mins ago

@Syfu_H Value Initialization. And I could be mistaken here (been caught on this in the past), but the Value Initialization is being replaced by Aggregate Initialization

– user4581301
31 mins ago

I recommend explaining why.

– user4581301
41 mins ago

Yes. Not onyl GCC but also MSVC14 also compiles Employee emp; but why?

– Syfu_H
39 mins ago

@Syfu_H Value Initialization. And I could be mistaken here (been caught on this in the past), but the Value Initialization is being replaced by Aggregate Initialization

– user4581301
31 mins ago

add a comment |

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