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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?

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7

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 1 hour ago

ypnos

37.2k1377113

asked 1 hour ago

gaurav bharadwajgaurav bharadwaj

507617

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @AndriyTylychko unique_ptr exist in boost too and behavior of that and std::unique_ptr has lot of similarity. Isn't it.
  
  – gaurav bharadwaj
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ypnos do you not agree with above comment of mine?
  
  – gaurav bharadwaj
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  For the record, clang does complain: godbolt.org/z/qEp6Ts
  
  – Max Langhof
  59 mins ago
  

  
  
  
  


• 
  
  
  

  
  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
  48 mins ago
  
  
  

  
  
  
  


• 
  
  
  

  
  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
  45 mins ago
  

  
  
  
  

 | 
show 5 more comments

7

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 1 hour ago

ypnos

37.2k1377113

asked 1 hour ago

gaurav bharadwajgaurav bharadwaj

507617

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @AndriyTylychko unique_ptr exist in boost too and behavior of that and std::unique_ptr has lot of similarity. Isn't it.
  
  – gaurav bharadwaj
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ypnos do you not agree with above comment of mine?
  
  – gaurav bharadwaj
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  For the record, clang does complain: godbolt.org/z/qEp6Ts
  
  – Max Langhof
  59 mins ago
  

  
  
  
  


• 
  
  
  

  
  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
  48 mins ago
  
  
  

  
  
  
  


• 
  
  
  

  
  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
  45 mins ago
  

  
  
  
  

 | 
show 5 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 1 hour ago

ypnos

37.2k1377113

asked 1 hour ago

gaurav bharadwajgaurav bharadwaj

507617

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 1 hour ago

ypnos

37.2k1377113

asked 1 hour ago

gaurav bharadwajgaurav bharadwaj

507617

share|improve this question

edited 1 hour ago

ypnos

37.2k1377113

asked 1 hour ago

gaurav bharadwajgaurav bharadwaj

507617

edited 1 hour ago

ypnos

37.2k1377113

edited 1 hour ago

ypnos

37.2k1377113

asked 1 hour ago

gaurav bharadwajgaurav bharadwaj

507617

asked 1 hour ago

gaurav bharadwajgaurav bharadwaj

507617

2 Answers
2

active

oldest

votes

12

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 58 mins ago

Michael KenzelMichael Kenzel

8,64811525

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That's a good find from GCC manual.
  
  – P.W
  35 mins ago
  

  
  
  
  

add a comment | 

6

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 55 mins ago

ArkadiyArkadiy

18.2k559102

add a comment | 

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12

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 58 mins ago

Michael KenzelMichael Kenzel

8,64811525

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That's a good find from GCC manual.
  
  – P.W
  35 mins ago
  

  
  
  
  

add a comment | 

12

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 58 mins ago

Michael KenzelMichael Kenzel

8,64811525

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  That's a good find from GCC manual.
  
  – P.W
  35 mins ago
  

  
  
  
  

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 58 mins ago

Michael KenzelMichael Kenzel

8,64811525

share|improve this answer

answered 58 mins ago

Michael KenzelMichael Kenzel

8,64811525

answered 58 mins ago

Michael KenzelMichael Kenzel

8,64811525

answered 58 mins ago

Michael KenzelMichael Kenzel

8,64811525

6

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 55 mins ago

ArkadiyArkadiy

18.2k559102

add a comment | 

6

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 55 mins ago

ArkadiyArkadiy

18.2k559102

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 55 mins ago

ArkadiyArkadiy

18.2k559102

share|improve this answer

answered 55 mins ago

ArkadiyArkadiy

18.2k559102

answered 55 mins ago

ArkadiyArkadiy

18.2k559102

answered 55 mins ago

ArkadiyArkadiy

18.2k559102