Extensions related to GNU C and C++

Certain language extensions that correspond to GNU C and C++ features are implemented to facilitate portability. These include extensions to C89, C99, C++98, and Standard C++. Throughout this document, the text indicates the IBM extensions that have been implemented for compatibility with GNU C and C++ ; a complete list of these is also provided in Appendix A. The IBM XL C language extensions and Appendix B. The IBM XL C++ language extensions.