The Header-to-copy utility ignores any data declaration it encounters unless it is defined as being external. If a C data declaration is defined as extern then the Header-to-copy utility generates a COBOL declaration using the IS EXTERNAL phrase.
If such an item is declared within a C module and the COBOL application can be linked to it, then the declaration allows the COBOL application to reference this C data item.
The Header-to-copy utility generates all output into the .cpy file except for external data declarations which are output to a separate .ext file.