Compiler Error C2504
Collapse the table of content
Expand the table of content
Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here. ArchiveDisclaimer

Compiler Error C2504

'class' : base class undefined

The base class is declared but never defined.

Possible cause

  • Missing include file.
  • External base class not declared with extern.

The following sample generates C2504:

// C2504.cpp
class A;
class B : public A
{   // C2504, define A before using it as a base class

int main()
© 2015 Microsoft