C++ copy constructor called at returnWhen to use virtual destructors?In which situations is the C++ copy constructor called?What are the differences between a pointer variable and a reference variable in C++?Why don't C++ compilers define operator== and operator!=?What is the lifetime of a static variable in a C++ function?Can I call a constructor from another constructor (do constructor chaining) in C++?Inheriting constructorsHow can I profile C++ code running on Linux?The Definitive C++ Book Guide and ListWhen to use virtual destructors?What is the “-->” operator in C++?What is the copy-and-swap idiom?
What are some good ways to treat frozen vegetables such that they behave like fresh vegetables when stir frying them?
Doesn't the system of the Supreme Court oppose justice?
"before" and "want" for the same systemd service?
Why do Radio Buttons not fill the entire outer circle?
What does "Scientists rise up against statistical significance" mean? (Comment in Nature)
Does Doodling or Improvising on the Piano Have Any Benefits?
Stack Interview Code methods made from class Node and Smart Pointers
Find the next value of this number series
The IT department bottlenecks progress, how should I handle this?
Shouldn’t conservatives embrace universal basic income?
How to preserve electronics (computers, iPads and phones) for hundreds of years
How to draw a matrix with arrows in limited space
Is it allowed to activate the ability of multiple planeswalkers in a single turn?
What (the heck) is a Super Worm Equinox Moon?
Are Captain Marvel's powers affected by Thanos breaking the Tesseract and claiming the stone?
What is the difference between lands and mana?
Will number of steps recorded on FitBit/any fitness tracker add up distance in PokemonGo?
How do I fix the group tension caused by my character stealing and possibly killing without provocation?
Is it ethical to recieve stipend after publishing enough papers?
Multiplicative persistence
What kind of floor tile is this?
Mimic lecturing on blackboard, facing audience
How do I tell my boss that I'm quitting soon, especially given that a colleague just left this week
PTIJ: Why is Haman obsessed with Bose?
C++ copy constructor called at return
When to use virtual destructors?In which situations is the C++ copy constructor called?What are the differences between a pointer variable and a reference variable in C++?Why don't C++ compilers define operator== and operator!=?What is the lifetime of a static variable in a C++ function?Can I call a constructor from another constructor (do constructor chaining) in C++?Inheriting constructorsHow can I profile C++ code running on Linux?The Definitive C++ Book Guide and ListWhen to use virtual destructors?What is the “-->” operator in C++?What is the copy-and-swap idiom?
error: use of deleted function 'A::A(const A&)'
return tmp;
^~~
Why is the copy constructor called only when there is a virtual destructor in A? How to avoid this?
struct B ;
struct A
std::unique_ptr<B> x;
virtual ~A() = default;
;
A f()
A tmp;
return tmp;
c++
asked 2 hours ago
SobuchSobuch
385
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
error: use of deleted function 'A::A(const A&)'
return tmp;
^~~
Why is the copy constructor called only when there is a virtual destructor in A? How to avoid this?
struct B ;
struct A
std::unique_ptr<B> x;
virtual ~A() = default;
;
A f()
A tmp;
return tmp;
c++
asked 2 hours ago
SobuchSobuch
385
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
see: In which situations is the C++ copy constructor called?
– kmdreko
1 hour ago
3
C++ handles objects different than C#/Java. When an instance goes out of scope (tmphere) its destructor must be called. Therefore, when youreturn tmpthen you're asking it to make a copy oftmpto be return to whomever calls the function. Once copied,tmpwill be destroyed and its copy will be available for use.
– Everyone
1 hour ago
add a comment |
error: use of deleted function 'A::A(const A&)'
return tmp;
^~~
Why is the copy constructor called only when there is a virtual destructor in A? How to avoid this?
struct B ;
struct A
std::unique_ptr<B> x;
virtual ~A() = default;
;
A f()
A tmp;
return tmp;
c++
asked 2 hours ago
SobuchSobuch
385
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
error: use of deleted function 'A::A(const A&)'
return tmp;
^~~
Why is the copy constructor called only when there is a virtual destructor in A? How to avoid this?
struct B ;
struct A
std::unique_ptr<B> x;
virtual ~A() = default;
;
A f()
A tmp;
return tmp;
c++
c++
asked 2 hours ago
SobuchSobuch
385
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
SobuchSobuch
385
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 1 hour ago
Sobuch
asked 2 hours ago
SobuchSobuch
385
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
SobuchSobuch
385
asked 2 hours ago
SobuchSobuch
385
385
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Sobuch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
see: In which situations is the C++ copy constructor called?
– kmdreko
1 hour ago
3
C++ handles objects different than C#/Java. When an instance goes out of scope (tmphere) its destructor must be called. Therefore, when youreturn tmpthen you're asking it to make a copy oftmpto be return to whomever calls the function. Once copied,tmpwill be destroyed and its copy will be available for use.
– Everyone
1 hour ago
add a comment |
see: In which situations is the C++ copy constructor called?
– kmdreko
1 hour ago
3
C++ handles objects different than C#/Java. When an instance goes out of scope (tmphere) its destructor must be called. Therefore, when youreturn tmpthen you're asking it to make a copy oftmpto be return to whomever calls the function. Once copied,tmpwill be destroyed and its copy will be available for use.
– Everyone
1 hour ago
see: In which situations is the C++ copy constructor called?
– kmdreko
1 hour ago
see: In which situations is the C++ copy constructor called?
– kmdreko
1 hour ago
3
3
C++ handles objects different than C#/Java. When an instance goes out of scope (
tmp here) its destructor must be called. Therefore, when you return tmp then you're asking it to make a copy of tmp to be return to whomever calls the function. Once copied, tmp will be destroyed and its copy will be available for use.– Everyone
1 hour ago
C++ handles objects different than C#/Java. When an instance goes out of scope (
tmp here) its destructor must be called. Therefore, when you return tmp then you're asking it to make a copy of tmp to be return to whomever calls the function. Once copied, tmp will be destroyed and its copy will be available for use.– Everyone
1 hour ago
add a comment |
1 Answer
1
active
oldest
votes
virtual ~A() = default; is a user declared destructor. Because of that, A no longer has a move constructor. That means return tmp; can't move tmp and since tmp is not copyable, you get a compiler error.
There are two ways you can fix this. You can add a move constructor like
struct A
std::unique_ptr<B> x;
A() = default; // you have to add this since the move constructor was added
A(A&&) = default; // defaulted move
virtual ~A() = default;
;
or you can create a base class that has the virtual destructor and inherit from that like
struct C
virtual ~C() = default;
;
struct A : C
std::unique_ptr<B> x;
;
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
5
Better to follow the Rule of Zero/Five. Either add all of (copy ctor, move ctor, copy assignment, move assignment, destructor) or add none of them. In this example, none of them are necessary.
– 0x5453
1 hour ago
1
@0x5453 Unless this is a parent class and the OP wants the derived classes to get destroyed properly. You need a virtual destructor if you have polymorphism.
– NathanOliver
1 hour ago
2
@Tzalumen no delete is required (because that's what the unique pointer does for you), but a virtual destructor is required so that the unique pointer won't have UB.
– eerorika
1 hour ago
3
@Tzalumen If youdeletean object of classXthrough a pointer to a base class ofXand that base class doesn't have a virtual dtor, it's Undefined Behaviour. Regardless of what the destructor does.
– Angew
1 hour ago
3
@Tzalumen If you have polymorphism, you must have a virtual destructor. If you don't the destructor for the derived class won't be called and you have UB.
– NathanOliver
1 hour ago
|
show 23 more comments
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
);
);
Sobuch is a new contributor. Be nice, and check out our Code of Conduct.
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%2f55288708%2fc-copy-constructor-called-at-return%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
virtual ~A() = default; is a user declared destructor. Because of that, A no longer has a move constructor. That means return tmp; can't move tmp and since tmp is not copyable, you get a compiler error.
There are two ways you can fix this. You can add a move constructor like
struct A
std::unique_ptr<B> x;
A() = default; // you have to add this since the move constructor was added
A(A&&) = default; // defaulted move
virtual ~A() = default;
;
or you can create a base class that has the virtual destructor and inherit from that like
struct C
virtual ~C() = default;
;
struct A : C
std::unique_ptr<B> x;
;
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
5
Better to follow the Rule of Zero/Five. Either add all of (copy ctor, move ctor, copy assignment, move assignment, destructor) or add none of them. In this example, none of them are necessary.
– 0x5453
1 hour ago
1
@0x5453 Unless this is a parent class and the OP wants the derived classes to get destroyed properly. You need a virtual destructor if you have polymorphism.
– NathanOliver
1 hour ago
2
@Tzalumen no delete is required (because that's what the unique pointer does for you), but a virtual destructor is required so that the unique pointer won't have UB.
– eerorika
1 hour ago
3
@Tzalumen If youdeletean object of classXthrough a pointer to a base class ofXand that base class doesn't have a virtual dtor, it's Undefined Behaviour. Regardless of what the destructor does.
– Angew
1 hour ago
3
@Tzalumen If you have polymorphism, you must have a virtual destructor. If you don't the destructor for the derived class won't be called and you have UB.
– NathanOliver
1 hour ago
|
show 23 more comments
virtual ~A() = default; is a user declared destructor. Because of that, A no longer has a move constructor. That means return tmp; can't move tmp and since tmp is not copyable, you get a compiler error.
There are two ways you can fix this. You can add a move constructor like
struct A
std::unique_ptr<B> x;
A() = default; // you have to add this since the move constructor was added
A(A&&) = default; // defaulted move
virtual ~A() = default;
;
or you can create a base class that has the virtual destructor and inherit from that like
struct C
virtual ~C() = default;
;
struct A : C
std::unique_ptr<B> x;
;
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
5
Better to follow the Rule of Zero/Five. Either add all of (copy ctor, move ctor, copy assignment, move assignment, destructor) or add none of them. In this example, none of them are necessary.
– 0x5453
1 hour ago
1
@0x5453 Unless this is a parent class and the OP wants the derived classes to get destroyed properly. You need a virtual destructor if you have polymorphism.
– NathanOliver
1 hour ago
2
@Tzalumen no delete is required (because that's what the unique pointer does for you), but a virtual destructor is required so that the unique pointer won't have UB.
– eerorika
1 hour ago
3
@Tzalumen If youdeletean object of classXthrough a pointer to a base class ofXand that base class doesn't have a virtual dtor, it's Undefined Behaviour. Regardless of what the destructor does.
– Angew
1 hour ago
3
@Tzalumen If you have polymorphism, you must have a virtual destructor. If you don't the destructor for the derived class won't be called and you have UB.
– NathanOliver
1 hour ago
|
show 23 more comments
virtual ~A() = default; is a user declared destructor. Because of that, A no longer has a move constructor. That means return tmp; can't move tmp and since tmp is not copyable, you get a compiler error.
There are two ways you can fix this. You can add a move constructor like
struct A
std::unique_ptr<B> x;
A() = default; // you have to add this since the move constructor was added
A(A&&) = default; // defaulted move
virtual ~A() = default;
;
or you can create a base class that has the virtual destructor and inherit from that like
struct C
virtual ~C() = default;
;
struct A : C
std::unique_ptr<B> x;
;
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
virtual ~A() = default; is a user declared destructor. Because of that, A no longer has a move constructor. That means return tmp; can't move tmp and since tmp is not copyable, you get a compiler error.
There are two ways you can fix this. You can add a move constructor like
struct A
std::unique_ptr<B> x;
A() = default; // you have to add this since the move constructor was added
A(A&&) = default; // defaulted move
virtual ~A() = default;
;
or you can create a base class that has the virtual destructor and inherit from that like
struct C
virtual ~C() = default;
;
struct A : C
std::unique_ptr<B> x;
;
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
edited 1 hour ago
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
answered 1 hour ago
NathanOliverNathanOliver
96k16136209
96k16136209
5
Better to follow the Rule of Zero/Five. Either add all of (copy ctor, move ctor, copy assignment, move assignment, destructor) or add none of them. In this example, none of them are necessary.
– 0x5453
1 hour ago
1
@0x5453 Unless this is a parent class and the OP wants the derived classes to get destroyed properly. You need a virtual destructor if you have polymorphism.
– NathanOliver
1 hour ago
2
@Tzalumen no delete is required (because that's what the unique pointer does for you), but a virtual destructor is required so that the unique pointer won't have UB.
– eerorika
1 hour ago
3
@Tzalumen If youdeletean object of classXthrough a pointer to a base class ofXand that base class doesn't have a virtual dtor, it's Undefined Behaviour. Regardless of what the destructor does.
– Angew
1 hour ago
3
@Tzalumen If you have polymorphism, you must have a virtual destructor. If you don't the destructor for the derived class won't be called and you have UB.
– NathanOliver
1 hour ago
|
show 23 more comments
5
Better to follow the Rule of Zero/Five. Either add all of (copy ctor, move ctor, copy assignment, move assignment, destructor) or add none of them. In this example, none of them are necessary.
– 0x5453
1 hour ago
1
@0x5453 Unless this is a parent class and the OP wants the derived classes to get destroyed properly. You need a virtual destructor if you have polymorphism.
– NathanOliver
1 hour ago
2
@Tzalumen no delete is required (because that's what the unique pointer does for you), but a virtual destructor is required so that the unique pointer won't have UB.
– eerorika
1 hour ago
3
@Tzalumen If youdeletean object of classXthrough a pointer to a base class ofXand that base class doesn't have a virtual dtor, it's Undefined Behaviour. Regardless of what the destructor does.
– Angew
1 hour ago
3
@Tzalumen If you have polymorphism, you must have a virtual destructor. If you don't the destructor for the derived class won't be called and you have UB.
– NathanOliver
1 hour ago
5
5
Better to follow the Rule of Zero/Five. Either add all of (copy ctor, move ctor, copy assignment, move assignment, destructor) or add none of them. In this example, none of them are necessary.
– 0x5453
1 hour ago
Better to follow the Rule of Zero/Five. Either add all of (copy ctor, move ctor, copy assignment, move assignment, destructor) or add none of them. In this example, none of them are necessary.
– 0x5453
1 hour ago
1
1
@0x5453 Unless this is a parent class and the OP wants the derived classes to get destroyed properly. You need a virtual destructor if you have polymorphism.
– NathanOliver
1 hour ago
@0x5453 Unless this is a parent class and the OP wants the derived classes to get destroyed properly. You need a virtual destructor if you have polymorphism.
– NathanOliver
1 hour ago
2
2
@Tzalumen no delete is required (because that's what the unique pointer does for you), but a virtual destructor is required so that the unique pointer won't have UB.
– eerorika
1 hour ago
@Tzalumen no delete is required (because that's what the unique pointer does for you), but a virtual destructor is required so that the unique pointer won't have UB.
– eerorika
1 hour ago
3
3
@Tzalumen If you
delete an object of class X through a pointer to a base class of X and that base class doesn't have a virtual dtor, it's Undefined Behaviour. Regardless of what the destructor does.– Angew
1 hour ago
@Tzalumen If you
delete an object of class X through a pointer to a base class of X and that base class doesn't have a virtual dtor, it's Undefined Behaviour. Regardless of what the destructor does.– Angew
1 hour ago
3
3
@Tzalumen If you have polymorphism, you must have a virtual destructor. If you don't the destructor for the derived class won't be called and you have UB.
– NathanOliver
1 hour ago
@Tzalumen If you have polymorphism, you must have a virtual destructor. If you don't the destructor for the derived class won't be called and you have UB.
– NathanOliver
1 hour ago
|
show 23 more comments
Sobuch is a new contributor. Be nice, and check out our Code of Conduct.
Sobuch is a new contributor. Be nice, and check out our Code of Conduct.
Sobuch is a new contributor. Be nice, and check out our Code of Conduct.
Sobuch is a new contributor. Be nice, and check out our Code of Conduct.
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%2f55288708%2fc-copy-constructor-called-at-return%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
see: In which situations is the C++ copy constructor called?
– kmdreko
1 hour ago
3
C++ handles objects different than C#/Java. When an instance goes out of scope (
tmphere) its destructor must be called. Therefore, when youreturn tmpthen you're asking it to make a copy oftmpto be return to whomever calls the function. Once copied,tmpwill be destroyed and its copy will be available for use.– Everyone
1 hour ago