The Question is:
As I can realize function popen in vaxc ?
The Answer is :
VAX C is a pre-ANSI C compiler and was entirely replaced by DEC C
(now known as Compaq C) many years ago.
Compaq C has popen available on V6.2 using the backport library, and
available native in the OpenVMS V7 and later C shareable library.
If you wish to continue to use VAX C, you will likely have some problems
with the non-ANSI C features of the compiler, as well as various potential
difficulties sharing code across OpenVMS Alpha and Tru64 UNIX systems,
with the complete lack of support for the compiler, with the lack of
updates for the compuler, and with the rather poor diagnostic support
available within the compiler.
Compaq C can be installed on the same OpenVMS VAX system with VAX C.