(Command-line option to suppress warning: -w-mpc) 

This warning is issued only if the -Vv option is in use. 

The warning may be issued when a member pointer to one type is cast to a member pointer of another type and the class of the converted member pointer has virtual bases. 

Encountering this warning means that at runtime, if the member pointer conversion cannot be completed, the result of the cast will be a NULL member pointer.