Use as undefined type error

幻之鬼舞者

I included the header file of class B in the header file of class A, and used a function of class A in the header file of class B. Compilation error: Undefined type A was used.
I added it in B's header file again; class A; still no.

gogoandsoso

Of course not, you can't use it that way. Use pointers or references instead.

不大会玩

Include class A header files in class B header files

lklklk

Add file header protection

engima

I guess it is your connection problem, not a compilation problem