Announced of classes inside one header when create file .msg in OMNeT++

[Ameera Al-harthi]

I have a problem when i create file.msg in OMNet++ .. we must be announced of any class we are used as the data type to packet variable.

cplusplus {{ #include "FieldFormat.h"}};

class fraCtrl extends void ; // syntx error

 class space extend void ; // syntx error

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the two classes inside #include "FieldFormat.h.