invalid new-expression of abstract class type

Question

I am currently writing a raytracer for a university class  In order to load Scenes from files I wrote an sdfloader to read sdf files and create scenes therefor   if I now want to compile the loader i get the following error   rc sdf loader cpp  In member function  void SDFloader  add shape std  istringstream amp     src sdf loader cpp 95 58  error  invalid new-expression of abstract class type  box                                   amp scene  materials mat                                                               I tried to find a solution but failed   The sdf loader class looks like the following   class SDFloader     public      SDFloader         SDFloader         Scene const amp  scene   const      void read std  string file      private      void add material std  istringstream amp        void add shape std  istringstream amp        void add light std  istringstream amp        void add camera std  istringstream amp        void apply transformation std  istringstream amp       private      Scene scene        in my implementation of the sdf loader i wrote the method read     void SDFloader  add shape std  istringstream amp  iss         std  string name      iss  gt  gt  name       if name     box           double x1 y1 z1 x2 y2 z2        std  string mat        iss  gt  gt  name  gt  gt  x1  gt  gt  y1  gt  gt  z1  gt  gt  x2  gt  gt  y2  gt  gt  z2  gt  gt  mat        scene  shapes insert new box point x1 y1 z1                                      point x2 y2 z2                                      name                                      amp scene  materials mat             and for every other shape the same calls   Where is the Problem in my code  I really don t see it  I am using g  -4 9 - std c  0x to compile and link everything

User · Answer

If you use C  11  you can use the specifier  override   and it will give you a compiler error if your aren t correctly overriding an abstract method   You probably have a method that doesn t match exactly with an abstract method in the base class  so your aren t actually overriding it   http   en cppreference com w cpp language override

User · Answer

Another possible cause for future Googlers  I had this issue because a method I was trying to implement required a std  unique ptr lt Queue gt  myQueue  as a parameter  but the Queue class is abstract  I solved that by using a QueuePtr myQueue  constructor like so   using QueuePtr   std  unique ptr lt Queue gt     and used that in the parameter list instead  This fixes it because the initializer tries to create a copy of Queue when you make a std  unique ptr of its type  which can t happen

User · Answer

invalid new-expression of abstract class type  box    There is nothing unclear about the error message  Your class box has at least one member that is not implemented  which means it is abstract  You cannot instantiate an abstract class   If this is a bug  fix your box class by implementing the missing member s     If it s by design  derive from box  implement the missing member s  and use the derived class

User · Answer

for others scratching their heads  I came across this error because I had innapropriately const-qualified one of the arguments to a method in a base class  so the derived class member functions were not over-riding it  so make sure you don t have something like  class Base      public        virtual void foo int a  const int b    0    class D  public Base     public       void foo int a  int b

[c++] invalid new-expression of abstract class type

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