I (SamJansen) was having a problem after making a C++ shared library. The error produced when I tried to run my application which loaded the library with dlopen(3) was

mylibrary.so: undefined symbol: __ti13INetTCPSocket

After using c++filt(1), we know the undefined symbol is the following

INetTCPSocket type_info node

InetTCPSocket is an abstract base class used as in interface. The reason this error was generated was because one function was not declared as abstract, I had forgotten the '= 0' part of the definition.

Another symptom of this is the linker complaining "vtable undefined for class x"