HP 3000 Manuals

HP C/iX Reference Manual

Non-ANSI Mode 

You may not want to change your existing code, or you may have old code
that relies on certain non-ANSI features.  Therefore, a non-ANSI mode of
compilation has been provided.  In this mode, virtually all programs that
compiled and executed under previous releases of HP C/iX will continue to
work as expected.

If you do not specify the mode of compilation, non-ANSI mode is the
default.  However, the default mode will be changed to ANSI on some
future release.

MPE/iX 5.0 Documentation