cocos2d-x编译错误问题

在xcode中创建的cocos2d-x项目，然后添加了一个基类，里面有虚方法，编译时出错，错误如下：

Undefined symbols for architecture x86_64:
  "typeinfo for BaseReader", referenced from:
      typeinfo for MainPageReader in MainPageReader.o
  "vtable for BaseReader", referenced from:
      BaseReader::BaseReader() in BaseReader.o
      BaseReader::BaseReader() in MainPageReader.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

问题其实是出在，基类中有的虚方法没有重写