Hi David, > What I am missing? Program in C, not in C-with-Microsoft-extensions. For interoperability between C and C++ for code and headers written in C, program in portable C. Portable C avoids all non-portable C-isms, C/C++ incompatibilities, and non-portable extensions. Portable C -- which is a coding convention / discipline -- also makes sure the headers have the extern "C" wrappers for C++, making them C++ savvy. Your use of unnamed structs data members does not comply with portable C, as it is considered a scoped forward declaration in C++ rather than a data member. To aid in writing portable C, enable all compiler warnings that you can. To aid in writing C / C++ interoperability, test-compiler your headers with the C++ compiler with all the warnings enabled to help you catch any C++ problems in your header files. Just putting in the extern "C" scope isn't enough, as there are some nuanced differences between C and C++. For information on portable C, use Google for "writing portable C". You may find hits on "Portable C Compiler" ... that's something else. HTH, --Eljay
