◄Up► ◄Contents► ◄Index► ◄Back► ──────────────────────────────────────────────────────────────────────────── Compiler error C2504 'class' : base class undefined The specified base class was declared but never defined. This error can be caused by a missing include file or an external base class that was not declared with the extern specifier. The following is an example of this error: class A; // error, A is undefined class A {}; // OK, A is defined class B : public A {}; // the error is detected here -♦-