Re: howto make system calls (newbie question)

["Marc A. Criley" <mcqada@earthlink.net>]

Lars Lundgren wrote:
> 
> On Fri, 4 May 2001, L.H.Jeong wrote:
> 
> >
> > procedure Command is
> >
> >    function C_System(value : String) return integer;
> >    pragma Import(
> >          C, C_System, "system");
> >
> >    result : integer;
> > begin
> >    result := C_System("pwd ");
> >    result := C_System(value => "acdsee D:\work\pictures\BP47.jpg ");
> > end Command;
> >
> >
> >
> 
> Thank you very much!
> 
> That does do the trick for me.
> 
> However i'm rather surprised to see you suggest that I escape ada and
> import C-functions. Is it really the case that such a (from my
> perspective) basic function can not be done solely in Ada - despite its
> extensive libraries?

"system" is neither part of C, nor part of Ada, it is an OS function
that uses a C-style calling syntax.

There's a widespread belief that OS functions, string handling
functions, and so on, are all part of C, which makes C so much more
powerful than languages like Ada.  In reality, all those functions are
provided in libraries for which C bindings have merely been provided by
the vendor.  The libraries themselves can be written in any programming
language, it is simply that a C-style calling syntax must be provided.

I've worked on a shared library, completely written in Ada, that is
invoked by C and Ada applications.  Even the Ada applications have to
use "pragma Import(C, ...)" to gain access to its functions.  (And of
course the library specifies pragma Export for the visible entities.)

Marc A. Criley
Senior Staff Engineer
Quadrus Corporation
www.quadruscorp.com