Why I cannot instantiate a class whose constructor is private in a friend class? Announcing...
Why is water being consumed when my shutoff valve is closed?
Marquee sign letters
Specify the range of GridLines
Determinant of a matrix with 2 equal rows
How to keep bees out of canned beverages?
Will I be more secure with my own router behind my ISP's router?
Is there a way to fake a method response using Mock or Stubs?
Is it accepted to use working hours to read general interest books?
false 'Security alert' from Google - every login generates mails from 'no-reply@accounts.google.com'
Is Bran literally the world's memory?
What is the evidence that custom checks in Northern Ireland are going to result in violence?
What is the ongoing value of the Kanban board to the developers as opposed to management
My admission is revoked after accepting the admission offer
Is there an efficient way for synchronising audio events real-time with LEDs using an MCU?
Processing ADC conversion result: DMA vs Processor Registers
What's called a person who work as someone who puts products on shelves in stores?
What is /etc/mtab in Linux?
What happened to Viserion in Season 7?
Why doesn't the university give past final exams' answers?
Is there a possibility to generate a list dynamically in Latex?
Why isn't everyone flabbergasted about Bran's "gift"?
How long can a nation maintain a technological edge over the rest of the world?
Not within Jobscope - Aggravated injury
How can I wire a 9-position switch so that each position turns on one more LED than the one before?
Why I cannot instantiate a class whose constructor is private in a friend class?
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30 pm US/Eastern)
Data science time! April 2019 and salary with experience
The Ask Question Wizard is Live!Can an abstract class have a constructor?Why do this() and super() have to be the first statement in a constructor?Why can't I change a private member of a class from a friend class in a different namespace?Passing a class as argument which has a private constructor that takes no parametersPrivate data members are inaccessible to friend functionFriend function is not accessing private members of another friend classDeclaring constructors as private shows errors. Is at least one public constructor mandatory?Cannot access private member declared in class, even declared friend classPrivate Data member is inaccessible in Friend FunctionPassing an object into the constructor of another class
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ height:90px;width:728px;box-sizing:border-box;
}
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 Salaryfrom being instantiated and onlyclass Employeecan instantiate it. So I declared the constructors ofSalaryprivate and madeEmployeefriend ofSalary. 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
mainfriend ofclass Salaryso 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
asked 1 hour ago
Syfu_HSyfu_H
35518
add a comment |
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 Salaryfrom being instantiated and onlyclass Employeecan instantiate it. So I declared the constructors ofSalaryprivate and madeEmployeefriend ofSalary. 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
mainfriend ofclass Salaryso 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
asked 1 hour ago
Syfu_HSyfu_H
35518
Why are you makingSalary's constructor private? It seems like there are contexts when you'd want to useSalaryoutside ofEmployee
– J. Antonio Perez
26 mins ago
add a comment |
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 Salaryfrom being instantiated and onlyclass Employeecan instantiate it. So I declared the constructors ofSalaryprivate and madeEmployeefriend ofSalary. 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
mainfriend ofclass Salaryso 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
asked 1 hour ago
Syfu_HSyfu_H
35518
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 Salaryfrom being instantiated and onlyclass Employeecan instantiate it. So I declared the constructors ofSalaryprivate and madeEmployeefriend ofSalary. 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
mainfriend ofclass Salaryso 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
c++ constructor friend-class
asked 1 hour ago
Syfu_HSyfu_H
35518
asked 1 hour ago
Syfu_HSyfu_H
35518
edited 1 hour ago
Syfu_H
asked 1 hour ago
Syfu_HSyfu_H
35518
asked 1 hour ago
Syfu_HSyfu_H
35518
asked 1 hour ago
Syfu_HSyfu_H
35518
35518
Why are you makingSalary's constructor private? It seems like there are contexts when you'd want to useSalaryoutside ofEmployee
– J. Antonio Perez
26 mins ago
add a comment |
Why are you makingSalary's constructor private? It seems like there are contexts when you'd want to useSalaryoutside ofEmployee
– J. Antonio Perez
26 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
26 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
26 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;
};
answered 50 mins ago
zdanzdan
22.1k34864
1
I'm trying on MSVS and onlyEmployee() {};allowsEmployee emp{};to compile. Clang seems to acceptEmployee() = default;, but then again, Clang seems to accept having no default constructor here.
– wally
33 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
23 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 52 mins ago
Raindrop7Raindrop7
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 41 mins ago
Pavan Manjunath
20.1k1181108
answered 1 hour ago
schuessschuess
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 1 hour ago
Eric SokolowskyEric Sokolowsky
514
1
I recommend explaining why.
– user4581301
1 hour ago
Yes. Not onyl GCC but also MSVC14 also compilesEmployee emp;but why?
– Syfu_H
58 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
50 mins ago
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55819962%2fwhy-i-cannot-instantiate-a-class-whose-constructor-is-private-in-a-friend-class%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
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;
};
answered 50 mins ago
zdanzdan
22.1k34864
1
I'm trying on MSVS and onlyEmployee() {};allowsEmployee emp{};to compile. Clang seems to acceptEmployee() = default;, but then again, Clang seems to accept having no default constructor here.
– wally
33 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
23 mins ago
add a comment |
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;
};
answered 50 mins ago
zdanzdan
22.1k34864
1
I'm trying on MSVS and onlyEmployee() {};allowsEmployee emp{};to compile. Clang seems to acceptEmployee() = default;, but then again, Clang seems to accept having no default constructor here.
– wally
33 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
23 mins ago
add a comment |
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;
};
answered 50 mins ago
zdanzdan
22.1k34864
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;
};
answered 50 mins ago
zdanzdan
22.1k34864
edited 35 mins ago
answered 50 mins ago
zdanzdan
22.1k34864
answered 50 mins ago
zdanzdan
22.1k34864
answered 50 mins ago
zdanzdan
22.1k34864
22.1k34864
1
I'm trying on MSVS and onlyEmployee() {};allowsEmployee emp{};to compile. Clang seems to acceptEmployee() = default;, but then again, Clang seems to accept having no default constructor here.
– wally
33 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
23 mins ago
add a comment |
1
I'm trying on MSVS and onlyEmployee() {};allowsEmployee emp{};to compile. Clang seems to acceptEmployee() = default;, but then again, Clang seems to accept having no default constructor here.
– wally
33 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
23 mins ago
1
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
33 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
33 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
23 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
23 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 52 mins ago
Raindrop7Raindrop7
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 52 mins ago
Raindrop7Raindrop7
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 52 mins ago
Raindrop7Raindrop7
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 52 mins ago
Raindrop7Raindrop7
3,74531224
answered 52 mins ago
Raindrop7Raindrop7
3,74531224
answered 52 mins ago
Raindrop7Raindrop7
3,74531224
answered 52 mins ago
Raindrop7Raindrop7
3,74531224
3,74531224
add a comment |
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 41 mins ago
Pavan Manjunath
20.1k1181108
answered 1 hour ago
schuessschuess
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 41 mins ago
Pavan Manjunath
20.1k1181108
answered 1 hour ago
schuessschuess
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 41 mins ago
Pavan Manjunath
20.1k1181108
answered 1 hour ago
schuessschuess
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 41 mins ago
Pavan Manjunath
20.1k1181108
answered 1 hour ago
schuessschuess
536416
edited 41 mins ago
Pavan Manjunath
20.1k1181108
edited 41 mins ago
Pavan Manjunath
20.1k1181108
edited 41 mins ago
Pavan Manjunath
20.1k1181108
20.1k1181108
answered 1 hour ago
schuessschuess
536416
answered 1 hour ago
schuessschuess
536416
answered 1 hour ago
schuessschuess
536416
536416
add a comment |
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 1 hour ago
Eric SokolowskyEric Sokolowsky
514
1
I recommend explaining why.
– user4581301
1 hour ago
Yes. Not onyl GCC but also MSVC14 also compilesEmployee emp;but why?
– Syfu_H
58 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
50 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 1 hour ago
Eric SokolowskyEric Sokolowsky
514
1
I recommend explaining why.
– user4581301
1 hour ago
Yes. Not onyl GCC but also MSVC14 also compilesEmployee emp;but why?
– Syfu_H
58 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
50 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 1 hour ago
Eric SokolowskyEric 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 1 hour ago
Eric SokolowskyEric Sokolowsky
514
answered 1 hour ago
Eric SokolowskyEric Sokolowsky
514
answered 1 hour ago
Eric SokolowskyEric Sokolowsky
514
answered 1 hour ago
Eric SokolowskyEric Sokolowsky
514
514
1
I recommend explaining why.
– user4581301
1 hour ago
Yes. Not onyl GCC but also MSVC14 also compilesEmployee emp;but why?
– Syfu_H
58 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
50 mins ago
add a comment |
1
I recommend explaining why.
– user4581301
1 hour ago
Yes. Not onyl GCC but also MSVC14 also compilesEmployee emp;but why?
– Syfu_H
58 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
50 mins ago
1
1
I recommend explaining why.
– user4581301
1 hour ago
I recommend explaining why.
– user4581301
1 hour ago
Yes. Not onyl GCC but also MSVC14 also compiles
Employee emp; but why?– Syfu_H
58 mins ago
Yes. Not onyl GCC but also MSVC14 also compiles
Employee emp; but why?– Syfu_H
58 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
50 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
50 mins ago
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55819962%2fwhy-i-cannot-instantiate-a-class-whose-constructor-is-private-in-a-friend-class%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Why are you making
Salary's constructor private? It seems like there are contexts when you'd want to useSalaryoutside ofEmployee– J. Antonio Perez
26 mins ago