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std::unique_ptr of base class holding reference of derived class does not show warning in gcc compiler while naked pointer shows it. Why?

Why unique-ptr doesn't check base class to virtual destructible?Does delete work with pointers to base class?Why does an overridden function in the derived class hide other overloads of the base class?Why simple destructor does not delete the derived object if declared using base pointerCalling a Derived Class method from a Void Pointer cast to a Base Objectclang & gcc don't warn about non-virtual base destructors for polymorphism when using smart pointers?Why is initialization of derived class through a base class pointer different from that through a derived class pointer?Destructor when derived class contains a pointer to base class objectUsing base class rather than base pointer to work on derived classHow to prevent a derived class object under base class pointer calling a public nonvirtual function defined in base class but overridden in derived?How can I convert std::make_unique<derived>() to std::unique_ptr<base>

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26

I have a hierarchy of base class and derived class. Base class has one virtual function which is overridden by derived class.

class Base
 
public: 
 ~Base(); 
 virtual void other_functionality() = 0; 
;

class Derived : public Base
 
public: 
 ~Derived (); 
 void other_functionality() //some code; 
;

Now if i do like this:

int main()

Base * P = new Derived ();
delete p;
return 0;

It gives error:
deleting object of polymorphic class type which has non-virtual destructor.

But with unique_ptr it passes without warning.

int main()

 std::unique_ptr<Base> p;
 p.reset(new Derived ());

return 0;

I know if I use virtual destructor. Warning with naked pointer will be solved. But question remains - why absence of virtual destructor shows problem with naked pointer and not with unique_ptr.

c++ c++14 gcc-warning

share|improve this question

edited Apr 25 at 12:09

ypnos

37.2k1377113

asked Apr 25 at 12:01

gaurav bharadwajgaurav bharadwaj

602719

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  For the record, clang does complain: godbolt.org/z/qEp6Ts
  
  – Max Langhof
  Apr 25 at 12:24
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @P.W I don't think this is a duplicate. At least, answers to both questions are different. (Answer to the original question is "because the Stadnard does not require such a check". Answer to this question is "because gcc supresses warnings for system headers".)
  
  – Daniel Langr
  Apr 25 at 12:35
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @DanielLangr: The question seemed the same in essence. But the answers do not directly address why the compiler does not issue a diagnostic. So I will reopen.
  
  – P.W
  Apr 25 at 12:38
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @gauravbharadwaj it's also in C++17 and pretty much guaranteed to be in C++20. I don't think this question is really specific to any particular version of the language at this point…
  
  – Michael Kenzel
  Apr 25 at 13:14
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @gauravbharadwaj I think it is fair that you tagged boost, and that other guy's comment was ridiculously worded. However I also believe the tag is wrong, this is a pure standard C++ matter and you do not even know about the existence of boost to answer this question.
  
  – ypnos
  2 days ago
  

  
  
  
  

 | 
show 6 more comments

26

I have a hierarchy of base class and derived class. Base class has one virtual function which is overridden by derived class.

class Base
 
public: 
 ~Base(); 
 virtual void other_functionality() = 0; 
;

class Derived : public Base
 
public: 
 ~Derived (); 
 void other_functionality() //some code; 
;

Now if i do like this:

int main()

Base * P = new Derived ();
delete p;
return 0;

It gives error:
deleting object of polymorphic class type which has non-virtual destructor.

But with unique_ptr it passes without warning.

int main()

 std::unique_ptr<Base> p;
 p.reset(new Derived ());

return 0;

I know if I use virtual destructor. Warning with naked pointer will be solved. But question remains - why absence of virtual destructor shows problem with naked pointer and not with unique_ptr.

c++ c++14 gcc-warning

share|improve this question

edited Apr 25 at 12:09

ypnos

37.2k1377113

asked Apr 25 at 12:01

gaurav bharadwajgaurav bharadwaj

602719

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  For the record, clang does complain: godbolt.org/z/qEp6Ts
  
  – Max Langhof
  Apr 25 at 12:24
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @P.W I don't think this is a duplicate. At least, answers to both questions are different. (Answer to the original question is "because the Stadnard does not require such a check". Answer to this question is "because gcc supresses warnings for system headers".)
  
  – Daniel Langr
  Apr 25 at 12:35
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @DanielLangr: The question seemed the same in essence. But the answers do not directly address why the compiler does not issue a diagnostic. So I will reopen.
  
  – P.W
  Apr 25 at 12:38
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @gauravbharadwaj it's also in C++17 and pretty much guaranteed to be in C++20. I don't think this question is really specific to any particular version of the language at this point…
  
  – Michael Kenzel
  Apr 25 at 13:14
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @gauravbharadwaj I think it is fair that you tagged boost, and that other guy's comment was ridiculously worded. However I also believe the tag is wrong, this is a pure standard C++ matter and you do not even know about the existence of boost to answer this question.
  
  – ypnos
  2 days ago
  

  
  
  
  

 | 
show 6 more comments

I have a hierarchy of base class and derived class. Base class has one virtual function which is overridden by derived class.

class Base
 
public: 
 ~Base(); 
 virtual void other_functionality() = 0; 
;

class Derived : public Base
 
public: 
 ~Derived (); 
 void other_functionality() //some code; 
;

Now if i do like this:

int main()

Base * P = new Derived ();
delete p;
return 0;

It gives error:
deleting object of polymorphic class type which has non-virtual destructor.

But with unique_ptr it passes without warning.

int main()

 std::unique_ptr<Base> p;
 p.reset(new Derived ());

return 0;

I know if I use virtual destructor. Warning with naked pointer will be solved. But question remains - why absence of virtual destructor shows problem with naked pointer and not with unique_ptr.

c++ c++14 gcc-warning

share|improve this question

edited Apr 25 at 12:09

ypnos

37.2k1377113

asked Apr 25 at 12:01

gaurav bharadwajgaurav bharadwaj

602719

class Base
 
public: 
 ~Base(); 
 virtual void other_functionality() = 0; 
;

class Derived : public Base
 
public: 
 ~Derived (); 
 void other_functionality() //some code; 
;

int main()

Base * P = new Derived ();
delete p;
return 0;

int main()

 std::unique_ptr<Base> p;
 p.reset(new Derived ());

return 0;

share|improve this question

edited Apr 25 at 12:09

ypnos

37.2k1377113

asked Apr 25 at 12:01

gaurav bharadwajgaurav bharadwaj

602719

share|improve this question

edited Apr 25 at 12:09

ypnos

37.2k1377113

asked Apr 25 at 12:01

gaurav bharadwajgaurav bharadwaj

602719

edited Apr 25 at 12:09

ypnos

37.2k1377113

edited Apr 25 at 12:09

ypnos

37.2k1377113

asked Apr 25 at 12:01

gaurav bharadwajgaurav bharadwaj

602719

asked Apr 25 at 12:01

gaurav bharadwajgaurav bharadwaj

602719

2 Answers
2

active

oldest

votes

31

Well, first of all, deleting a derived object through a base pointer when the base class does not have a virtual destructor is undefined behavior. Compilers are not required to diagnose undefined behavior…

That being said, the reason why this warning does not appear when using std::unique_ptr is most likely due to the fact that GCC does not report warnings that would appear in system headers.

share|improve this answer

answered Apr 25 at 12:24

Michael KenzelMichael Kenzel

8,91311625

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  That's a good find from GCC manual.
  
  – P.W
  Apr 25 at 12:48
  

  
  
  
  

add a comment | 

18

I cannot find a link, but I did see a discussion of this online, in GCC bug database.

The warning is issued on the actual delete expression. In the case of unique_ptr, the delete is called inside a system header file.

According to the discussion in that bug report, implementing C++ system libraries requires all sorts of compromises that result in various warnings. Therefore, the warnings are restricted inside system headers. That is the reason you won't see the warning you expect.

Update: and here it is, straight from the horse's mouth:

https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html

The header files declaring interfaces to the operating system and runtime libraries often cannot be written in strictly conforming C. Therefore, GCC gives code found in system headers special treatment. All warnings, other than those generated by ‘#warning’ (see Diagnostics), are suppressed while GCC is processing a system header.

share|improve this answer

answered Apr 25 at 12:28

ArkadiyArkadiy

18.3k559103

add a comment | 

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31

Well, first of all, deleting a derived object through a base pointer when the base class does not have a virtual destructor is undefined behavior. Compilers are not required to diagnose undefined behavior…

That being said, the reason why this warning does not appear when using std::unique_ptr is most likely due to the fact that GCC does not report warnings that would appear in system headers.

share|improve this answer

answered Apr 25 at 12:24

Michael KenzelMichael Kenzel

8,91311625

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  That's a good find from GCC manual.
  
  – P.W
  Apr 25 at 12:48
  

  
  
  
  

add a comment | 

31

Well, first of all, deleting a derived object through a base pointer when the base class does not have a virtual destructor is undefined behavior. Compilers are not required to diagnose undefined behavior…

That being said, the reason why this warning does not appear when using std::unique_ptr is most likely due to the fact that GCC does not report warnings that would appear in system headers.

share|improve this answer

answered Apr 25 at 12:24

Michael KenzelMichael Kenzel

8,91311625

• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  That's a good find from GCC manual.
  
  – P.W
  Apr 25 at 12:48
  

  
  
  
  

add a comment | 

Well, first of all, deleting a derived object through a base pointer when the base class does not have a virtual destructor is undefined behavior. Compilers are not required to diagnose undefined behavior…

That being said, the reason why this warning does not appear when using std::unique_ptr is most likely due to the fact that GCC does not report warnings that would appear in system headers.

share|improve this answer

answered Apr 25 at 12:24

Michael KenzelMichael Kenzel

8,91311625

share|improve this answer

answered Apr 25 at 12:24

Michael KenzelMichael Kenzel

8,91311625

answered Apr 25 at 12:24

Michael KenzelMichael Kenzel

8,91311625

answered Apr 25 at 12:24

Michael KenzelMichael Kenzel

8,91311625

18

I cannot find a link, but I did see a discussion of this online, in GCC bug database.

The warning is issued on the actual delete expression. In the case of unique_ptr, the delete is called inside a system header file.

According to the discussion in that bug report, implementing C++ system libraries requires all sorts of compromises that result in various warnings. Therefore, the warnings are restricted inside system headers. That is the reason you won't see the warning you expect.

Update: and here it is, straight from the horse's mouth:

https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html

The header files declaring interfaces to the operating system and runtime libraries often cannot be written in strictly conforming C. Therefore, GCC gives code found in system headers special treatment. All warnings, other than those generated by ‘#warning’ (see Diagnostics), are suppressed while GCC is processing a system header.

share|improve this answer

answered Apr 25 at 12:28

ArkadiyArkadiy

18.3k559103

add a comment | 

18

I cannot find a link, but I did see a discussion of this online, in GCC bug database.

The warning is issued on the actual delete expression. In the case of unique_ptr, the delete is called inside a system header file.

According to the discussion in that bug report, implementing C++ system libraries requires all sorts of compromises that result in various warnings. Therefore, the warnings are restricted inside system headers. That is the reason you won't see the warning you expect.

Update: and here it is, straight from the horse's mouth:

https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html

The header files declaring interfaces to the operating system and runtime libraries often cannot be written in strictly conforming C. Therefore, GCC gives code found in system headers special treatment. All warnings, other than those generated by ‘#warning’ (see Diagnostics), are suppressed while GCC is processing a system header.

share|improve this answer

answered Apr 25 at 12:28

ArkadiyArkadiy

18.3k559103

add a comment | 

I cannot find a link, but I did see a discussion of this online, in GCC bug database.

The warning is issued on the actual delete expression. In the case of unique_ptr, the delete is called inside a system header file.

According to the discussion in that bug report, implementing C++ system libraries requires all sorts of compromises that result in various warnings. Therefore, the warnings are restricted inside system headers. That is the reason you won't see the warning you expect.

Update: and here it is, straight from the horse's mouth:

https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html

The header files declaring interfaces to the operating system and runtime libraries often cannot be written in strictly conforming C. Therefore, GCC gives code found in system headers special treatment. All warnings, other than those generated by ‘#warning’ (see Diagnostics), are suppressed while GCC is processing a system header.

share|improve this answer

answered Apr 25 at 12:28

ArkadiyArkadiy

18.3k559103

share|improve this answer

answered Apr 25 at 12:28

ArkadiyArkadiy

18.3k559103

answered Apr 25 at 12:28

ArkadiyArkadiy

18.3k559103

answered Apr 25 at 12:28

ArkadiyArkadiy

18.3k559103