g undefined reference to typeinfo

Question

I just ran across the following error  and found the solution online  but it s not present in Stack Overflow         gnu linkonce  stuff    undefined   reference to  method   object   file    gnu linkonce  stuff      undefined reference to  typeinfo for    classname     Why might one get one of these  undefined reference to typeinfo  linker errors    Bonus points if you can explain what s going on behind the scenes

User · Answer

I ve got same error when my interface  with all pure virtual functions  needed one more function and I forgot to  null  it   I had  class ICommProvider   public                  brief If connection is established  it sends the message into the server          param in  msg - message to be send         return    0 if success  error otherwise             virtual int vaSend const std  string  amp msg    0                  brief If connection is established  it is waiting will server response back          param out  msg is the message received from server         return     0 if success  error otherwise             virtual int vaReceive std  string  amp msg    0      virtual int vaSendRaw const char  buff  int bufflen    0      virtual int vaReceiveRaw char  buff  int bufflen    0                  bief Closes current connection  if needed  after serving         return 0 if success  error otherwise             virtual int vaClose        Last vaClose is not virtual so compiled did not know where to get implementation for it and thereby got confused  my message was         TCPClient o   rodata 0x38   undefined reference to  typeinfo for ICommProvider    Simple change from  virtual int vaClose      to  virtual int vaClose     0    fixed the problem  hope it helps

User · Answer

Quoting from the gcc manual      For polymorphic classes  classes with virtual functions   the type info object is written out along with the vtable       For all other types  we write out the type info object when it is used  when applying  typeid  to an expression  throwing an object  or referring to a type in a catch clause or exception specification    And a bit earlier on the same page      If the class declares any non-inline  non-pure virtual functions  the first one is chosen as the    key method    for the class  and the vtable is only emitted in the translation unit where the key method is defined    So  this error happens when the  key method  is missing its definition  as other answers already mentioned

User · Answer

I just spent a few hours on this error  and while the other answers here helped me understand what was going on  they did not fix my particular problem    I am working on a project that compiles using both clang   and g    I was having no linking issues using clang    but was getting the undefined reference to  typeinfo for error with g     The important point  Linking order MATTERS with g    If you list the libraries you want to link in an order which is incorrect you can get the typeinfo error   See this SO question for more details on linking order with gcc g

User · Answer

This occurs when declared  non-pure  virtual functions are missing bodies  In your class definition  something like   virtual void foo      Should be defined  inline or in a linked source file    virtual void foo        Or declared pure virtual   virtual void foo     0

User · Answer

Quoting from the gcc manual      For polymorphic classes  classes with virtual functions   the type info object is written out along with the vtable       For all other types  we write out the type info object when it is used  when applying  typeid  to an expression  throwing an object  or referring to a type in a catch clause or exception specification    And a bit earlier on the same page      If the class declares any non-inline  non-pure virtual functions  the first one is chosen as the    key method    for the class  and the vtable is only emitted in the translation unit where the key method is defined    So  this error happens when the  key method  is missing its definition  as other answers already mentioned

User · Answer

The previous answers are correct  but this error can also be caused by attempting to use typeid on an object of a class that has no virtual functions  C   RTTI requires a vtable  so classes that you wish to perform type identification on require at least one virtual function    If you want type information to work on a class for which you don t really want any virtual functions  make the destructor virtual

User · Answer

Check that your dependencies were compiled without -f-nortti   For some projects you have to set it explicitly  like in RocksDB   USE RTTI 1 make shared lib -j4

User · Answer

This occurs when declared  non-pure  virtual functions are missing bodies  In your class definition  something like   virtual void foo      Should be defined  inline or in a linked source file    virtual void foo        Or declared pure virtual   virtual void foo     0

User · Answer

in my case  i used a third-party library with header files and so file  i subclassed one class  and link error like this occurred when i try to instantiate my subclass   as mentioned by  sergiy  knowning it could be the problem of  rtti   i managed to workaround it by put the constructor implementation into separate  cpp file and apply  -fno-rtti  compile flags to the file  it works well   as i am still not quite clear about the internal of this link error  i am not sure whether my solution is general  however  i think it worth a shot before trying the adaptor way as mentioned by  francois   and of course  if all source codes are available not in my case   better do recompile with  -frtti  if possible   one more thing  if you choose to try my solution  try make the separate file as simple as possible  and do not use some fancy features of C    take special attention on boost related things  cause much of it depends on rtti

User · Answer

In my case it was a virtual function in an interface class that wasn t defined as a pure virtual   class IInterface   public    virtual void Foo     0      I forgot the   0 bit

User · Answer

One possible reason is because you are declaring a virtual function without defining it   When you declare it without defining it in the same compilation unit  you re indicating that it s defined somewhere else - this means the linker phase will try to find it in one of the other compilation units  or libraries    An example of defining the virtual function is   virtual void fn        insert code here        In this case  you are attaching a definition to the declaration  which means the linker doesn t need to resolve it later   The line  virtual void fn      declares fn   without defining it and will cause the error message you asked about   It s very similar to the code   extern int i  int  pi    amp i    which states that the integer i is declared in another compilation unit which must be resolved at link time  otherwise pi can t be set to it s address

User · Answer

This can also happen when you mix -fno-rtti and -frtti code  Then you need to ensure that any class  which type info is accessed in the -frtti code  have their key method compiled with -frtti  Such access can happen when you create an object of the class  use dynamic cast etc    source

User · Answer

The previous answers are correct  but this error can also be caused by attempting to use typeid on an object of a class that has no virtual functions  C   RTTI requires a vtable  so classes that you wish to perform type identification on require at least one virtual function    If you want type information to work on a class for which you don t really want any virtual functions  make the destructor virtual

User · Answer

One possible reason is because you are declaring a virtual function without defining it   When you declare it without defining it in the same compilation unit  you re indicating that it s defined somewhere else - this means the linker phase will try to find it in one of the other compilation units  or libraries    An example of defining the virtual function is   virtual void fn        insert code here        In this case  you are attaching a definition to the declaration  which means the linker doesn t need to resolve it later   The line  virtual void fn      declares fn   without defining it and will cause the error message you asked about   It s very similar to the code   extern int i  int  pi    amp i    which states that the integer i is declared in another compilation unit which must be resolved at link time  otherwise pi can t be set to it s address

User · Answer

If you re linking one  so to another  yet one more possibility is compiling with  -fvisibility hidden  in gcc or g     If both  so files were built with  -fvisibility hidden  and the key method is not in the same  so as another of the virtual function s implementations  the latter won t see the vtable or typeinfo of the former   To the linker  this looks like an unimplemented virtual function  as in paxdiablo s and cdleary s answers    In this case  you must make an exception for the visibility of the base class with     attribute     visibility  default       in the class declaration   For instance   class   attribute     visibility  default     boom      virtual void stick        Another solution  of course  is to not use  -fvisibility hidden    That does complicate things for the compiler and linker  possibly to the detriment of code performance

User · Answer

In the base class  an abstract base class  you declare a virtual destructor and as you cannot declare a destructor as a pure virtual function   either you have to define it right here in the abstract class  just a dummy definition like virtual  base       will do  or in any of the derived class   If you fail to do this  you will end up in an  undefined symbol  at link time  Since VMT has an entry for all the pure virtual functions with a matching NULL as it updates the table depending on the implementation in the derived class  But for the non-pure but virtual functions  it needs the definition at the link time so that it can update the VMT table   Use c  filt to demangle the symbol  Like  c  filt  ZTIN10storageapi8BaseHostE will output something like  typeinfo for storageapi  BaseHost

User · Answer

Check that your dependencies were compiled without -f-nortti   For some projects you have to set it explicitly  like in RocksDB   USE RTTI 1 make shared lib -j4

User · Answer

I got a lot of these errors just now  What happened is that I split a header-file-only class into a header file and a cpp file  However  I didn t update my build system  so the cpp file didn t get compiled  Among simply having undefined references to the functions declared in the header but not implemented  I got a lot of these typeinfo errors    The solution was to re-run the build system to compile and link the new cpp file

User · Answer

The previous answers are correct  but this error can also be caused by attempting to use typeid on an object of a class that has no virtual functions  C   RTTI requires a vtable  so classes that you wish to perform type identification on require at least one virtual function    If you want type information to work on a class for which you don t really want any virtual functions  make the destructor virtual

User · Answer

in my case  i used a third-party library with header files and so file  i subclassed one class  and link error like this occurred when i try to instantiate my subclass   as mentioned by  sergiy  knowning it could be the problem of  rtti   i managed to workaround it by put the constructor implementation into separate  cpp file and apply  -fno-rtti  compile flags to the file  it works well   as i am still not quite clear about the internal of this link error  i am not sure whether my solution is general  however  i think it worth a shot before trying the adaptor way as mentioned by  francois   and of course  if all source codes are available not in my case   better do recompile with  -frtti  if possible   one more thing  if you choose to try my solution  try make the separate file as simple as possible  and do not use some fancy features of C    take special attention on boost related things  cause much of it depends on rtti

User · Answer

I just spent a few hours on this error  and while the other answers here helped me understand what was going on  they did not fix my particular problem    I am working on a project that compiles using both clang   and g    I was having no linking issues using clang    but was getting the undefined reference to  typeinfo for error with g     The important point  Linking order MATTERS with g    If you list the libraries you want to link in an order which is incorrect you can get the typeinfo error   See this SO question for more details on linking order with gcc g

User · Answer

In my case it was a virtual function in an interface class that wasn t defined as a pure virtual   class IInterface   public    virtual void Foo     0      I forgot the   0 bit

User · Answer

Similarly to the RTTI  NO-RTTI discussion above  this problem can also occur if you use dynamic cast and fail to include the object code containing the class implementation   I ran into this problem building on Cygwin and then porting code to Linux  The make files  directory structure and even the gcc versions  4 8 2  were identical in both cases  but the code linked and operated correctly on Cygwin but failed to link on Linux  Red Hat Cygwin has apparently made compiler linker modifications that avoid the object code linking requirement   The Linux linker error message properly directed me to the dynamic cast line  but earlier messages in this forum had me looking for missing function implementations rather than the actual problem  missing object code  My workaround was to substitute a virtual type function in the base and derived class  e g  virtual int isSpecialType    rather than use dynamic cast  This technique avoids the requirement to link object implementation code just to get dynamic cast to work properly

User · Answer

In  my case it is purely a library dependency issue even if I have dynamic cast call  After adding enough dependency into makefile this problem was gone

User · Answer

Quoting from the gcc manual      For polymorphic classes  classes with virtual functions   the type info object is written out along with the vtable       For all other types  we write out the type info object when it is used  when applying  typeid  to an expression  throwing an object  or referring to a type in a catch clause or exception specification    And a bit earlier on the same page      If the class declares any non-inline  non-pure virtual functions  the first one is chosen as the    key method    for the class  and the vtable is only emitted in the translation unit where the key method is defined    So  this error happens when the  key method  is missing its definition  as other answers already mentioned

User · Answer

Quoting from the gcc manual      For polymorphic classes  classes with virtual functions   the type info object is written out along with the vtable       For all other types  we write out the type info object when it is used  when applying  typeid  to an expression  throwing an object  or referring to a type in a catch clause or exception specification    And a bit earlier on the same page      If the class declares any non-inline  non-pure virtual functions  the first one is chosen as the    key method    for the class  and the vtable is only emitted in the translation unit where the key method is defined    So  this error happens when the  key method  is missing its definition  as other answers already mentioned

User · Answer

The previous answers are correct  but this error can also be caused by attempting to use typeid on an object of a class that has no virtual functions  C   RTTI requires a vtable  so classes that you wish to perform type identification on require at least one virtual function    If you want type information to work on a class for which you don t really want any virtual functions  make the destructor virtual

User · Answer

One possible reason is because you are declaring a virtual function without defining it   When you declare it without defining it in the same compilation unit  you re indicating that it s defined somewhere else - this means the linker phase will try to find it in one of the other compilation units  or libraries    An example of defining the virtual function is   virtual void fn        insert code here        In this case  you are attaching a definition to the declaration  which means the linker doesn t need to resolve it later   The line  virtual void fn      declares fn   without defining it and will cause the error message you asked about   It s very similar to the code   extern int i  int  pi    amp i    which states that the integer i is declared in another compilation unit which must be resolved at link time  otherwise pi can t be set to it s address

User · Answer

I encounter an situation that is rare  but this may help other friends in similar situation   I have to work on an older system with gcc 4 4 7   I have to compile code with c  11 or above support  so I build the latest version of gcc 5 3 0  When building my code and linking to the dependencies if the dependency is build with older compiler  then I got  undefined reference to  error even though I clearly defined the linking path with -L path to lib -llibname   Some packages such as boost and projects build with cmake usually has a tendency to use the older compiler  and they usually cause such problems  You have to go a long way to make sure they use the newer compiler

User · Answer

Possible solutions for code that deal with RTTI and non-RTTI libraries   a  Recompile everything with either -frtti or -fno-rtti  b  If a  is not possible for you  try the following   Assume libfoo is built without RTTI  Your code uses libfoo and compiles with RTTI  If you use a class  Foo  in libfoo that has virtuals  you re likely to run into a link-time error that says  missing typeinfo for class Foo   Define another class  e g  FooAdapter  that has no virtual and will forward calls to Foo that you use   Compile FooAdapter in a small static library that doesn t use RTTI and only depends on libfoo symbols  Provide a header for it and use that instead in your code  which uses RTTI   Since FooAdapter has no virtual function it won t have any typeinfo and you ll be able to link your binary  If you use a lot of different classes from libfoo  this solution may not be convenient  but it s a start

User · Answer

If you re linking one  so to another  yet one more possibility is compiling with  -fvisibility hidden  in gcc or g     If both  so files were built with  -fvisibility hidden  and the key method is not in the same  so as another of the virtual function s implementations  the latter won t see the vtable or typeinfo of the former   To the linker  this looks like an unimplemented virtual function  as in paxdiablo s and cdleary s answers    In this case  you must make an exception for the visibility of the base class with     attribute     visibility  default       in the class declaration   For instance   class   attribute     visibility  default     boom      virtual void stick        Another solution  of course  is to not use  -fvisibility hidden    That does complicate things for the compiler and linker  possibly to the detriment of code performance

User · Answer

In  my case it is purely a library dependency issue even if I have dynamic cast call  After adding enough dependency into makefile this problem was gone

User · Answer

Similarly to the RTTI  NO-RTTI discussion above  this problem can also occur if you use dynamic cast and fail to include the object code containing the class implementation   I ran into this problem building on Cygwin and then porting code to Linux  The make files  directory structure and even the gcc versions  4 8 2  were identical in both cases  but the code linked and operated correctly on Cygwin but failed to link on Linux  Red Hat Cygwin has apparently made compiler linker modifications that avoid the object code linking requirement   The Linux linker error message properly directed me to the dynamic cast line  but earlier messages in this forum had me looking for missing function implementations rather than the actual problem  missing object code  My workaround was to substitute a virtual type function in the base and derived class  e g  virtual int isSpecialType    rather than use dynamic cast  This technique avoids the requirement to link object implementation code just to get dynamic cast to work properly

User · Answer

Possible solutions for code that deal with RTTI and non-RTTI libraries   a  Recompile everything with either -frtti or -fno-rtti  b  If a  is not possible for you  try the following   Assume libfoo is built without RTTI  Your code uses libfoo and compiles with RTTI  If you use a class  Foo  in libfoo that has virtuals  you re likely to run into a link-time error that says  missing typeinfo for class Foo   Define another class  e g  FooAdapter  that has no virtual and will forward calls to Foo that you use   Compile FooAdapter in a small static library that doesn t use RTTI and only depends on libfoo symbols  Provide a header for it and use that instead in your code  which uses RTTI   Since FooAdapter has no virtual function it won t have any typeinfo and you ll be able to link your binary  If you use a lot of different classes from libfoo  this solution may not be convenient  but it s a start

User · Answer

I encounter an situation that is rare  but this may help other friends in similar situation   I have to work on an older system with gcc 4 4 7   I have to compile code with c  11 or above support  so I build the latest version of gcc 5 3 0  When building my code and linking to the dependencies if the dependency is build with older compiler  then I got  undefined reference to  error even though I clearly defined the linking path with -L path to lib -llibname   Some packages such as boost and projects build with cmake usually has a tendency to use the older compiler  and they usually cause such problems  You have to go a long way to make sure they use the newer compiler

User · Answer

This occurs when declared  non-pure  virtual functions are missing bodies  In your class definition  something like   virtual void foo      Should be defined  inline or in a linked source file    virtual void foo        Or declared pure virtual   virtual void foo     0

User · Answer

I got a lot of these errors just now  What happened is that I split a header-file-only class into a header file and a cpp file  However  I didn t update my build system  so the cpp file didn t get compiled  Among simply having undefined references to the functions declared in the header but not implemented  I got a lot of these typeinfo errors    The solution was to re-run the build system to compile and link the new cpp file

User · Answer

In the base class  an abstract base class  you declare a virtual destructor and as you cannot declare a destructor as a pure virtual function   either you have to define it right here in the abstract class  just a dummy definition like virtual  base       will do  or in any of the derived class   If you fail to do this  you will end up in an  undefined symbol  at link time  Since VMT has an entry for all the pure virtual functions with a matching NULL as it updates the table depending on the implementation in the derived class  But for the non-pure but virtual functions  it needs the definition at the link time so that it can update the VMT table   Use c  filt to demangle the symbol  Like  c  filt  ZTIN10storageapi8BaseHostE will output something like  typeinfo for storageapi  BaseHost

User · Answer

This occurs when declared  non-pure  virtual functions are missing bodies  In your class definition  something like   virtual void foo      Should be defined  inline or in a linked source file    virtual void foo        Or declared pure virtual   virtual void foo     0

User · Answer

This can also happen when you mix -fno-rtti and -frtti code  Then you need to ensure that any class  which type info is accessed in the -frtti code  have their key method compiled with -frtti  Such access can happen when you create an object of the class  use dynamic cast etc    source

User · Answer

I ve got same error when my interface  with all pure virtual functions  needed one more function and I forgot to  null  it   I had  class ICommProvider   public                  brief If connection is established  it sends the message into the server          param in  msg - message to be send         return    0 if success  error otherwise             virtual int vaSend const std  string  amp msg    0                  brief If connection is established  it is waiting will server response back          param out  msg is the message received from server         return     0 if success  error otherwise             virtual int vaReceive std  string  amp msg    0      virtual int vaSendRaw const char  buff  int bufflen    0      virtual int vaReceiveRaw char  buff  int bufflen    0                  bief Closes current connection  if needed  after serving         return 0 if success  error otherwise             virtual int vaClose        Last vaClose is not virtual so compiled did not know where to get implementation for it and thereby got confused  my message was         TCPClient o   rodata 0x38   undefined reference to  typeinfo for ICommProvider    Simple change from  virtual int vaClose      to  virtual int vaClose     0    fixed the problem  hope it helps

User · Answer

One possible reason is because you are declaring a virtual function without defining it   When you declare it without defining it in the same compilation unit  you re indicating that it s defined somewhere else - this means the linker phase will try to find it in one of the other compilation units  or libraries    An example of defining the virtual function is   virtual void fn        insert code here        In this case  you are attaching a definition to the declaration  which means the linker doesn t need to resolve it later   The line  virtual void fn      declares fn   without defining it and will cause the error message you asked about   It s very similar to the code   extern int i  int  pi    amp i    which states that the integer i is declared in another compilation unit which must be resolved at link time  otherwise pi can t be set to it s address

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