binding to C: popen

binding to C: popen

[Poul-Erik Andreasen]

Hi

i am trying to make a biding to the C function popen, it goes like this:

with System.Address_To_Access_Conversions;
with Interfaces.C_Streams;

package Pipe_Pkg is

    subtype Command_Pipe is Interfaces.C_Streams.FILEs;

    procedure Pipe_Open (Pipe    : in out Command_Pipe;
                         Command : in  String);
private

   function To_C (Input : in String) return Interfaces.C_Streams.Chars;

end Pipe_Pkg;


package body Pipe_Pkg is


    procedure Pipe_Open
      (Pipe    : in out Command_Pipe;
       Command : in  String)
    is
       use Interfaces.C_Streams;
       function C_Popen (C_Command : Chars;
                         C_Type    : Chars) return Command_Pipe;

       pragma Import (C, C_Popen, "popen");

    begin
       Pipe := C_Popen ((To_C (Command)), To_C ("w"));
    end Pipe_Open;

    function To_C (Input : in String) return Interfaces.C_Streams.Chars 


    is
      package String_Conversion is
         new System.Address_To_Access_Conversions (String);

      String_Pointer : String_Conversion.Object_Pointer :=
                          new String'(Input & ascii.nul);
    begin
       return String_Conversion.To_Address (String_Pointer);
    end;


end Pipe_Pkg;



This ictually going as it is suppose to, but i would like set in an 
exception if the piping dosn't have succes. Acording to the C manual
popen returns null if it fails. But how do i test on that in the FILEs type?

Re: binding to C: popen

[jimmaureenrogers]

Poul-Erik Andreasen wrote:
> This ictually going as it is suppose to, but i would like set in an
> exception if the piping dosn't have succes. Acording to the C manual
> popen returns null if it fails. But how do i test on that in the FILEs type?

The popen man page describes the command as:
FILE *popen(const char *command, const char *mode);

Note that popen returns a file pointer. Upon failure it returns a null
pointer.

It seems that you might be able to test if the return value is null.

Jim Rogers

Re: binding to C: popen

[Poul-Erik Andreasen]

jimmaureenrogers@worldnet.att.net wrote:
> Poul-Erik Andreasen wrote:
> 
>>This ictually going as it is suppose to, but i would like set in an
>>exception if the piping dosn't have succes. Acording to the C manual
>>popen returns null if it fails. But how do i test on that in the FILEs type?
> 
> 
> The popen man page describes the command as:
> FILE *popen(const char *command, const char *mode);
> 
> Note that popen returns a file pointer. Upon failure it returns a null
> pointer.
> 
> It seems that you might be able to test if the return value is null.
> 
> Jim Rogers
> 

Yes but a C pointer is in Ada represented as system.address and i can 
not test that for O the the systems.address_image gives 0804C060 and if 
that is a stadart c value for a null-pointer things are fine, but that 
seems to be a hack.


Poul-Erik

Re: binding to C: popen

[Georg Bauhaus]

Poul-Erik Andreasen wrote:

> Yes but a C pointer is in Ada represented as system.address and i can
> not test that for O the the systems.address_image gives 0804C060 and if
> that is a stadart c value for a null-pointer things are fine, but that
> seems to be a hack.

System.Null_Address, or Interfaces.C.Strings.Null_Ptr perhaps?

You could consider writing a predicate like

  fucntion is_null(p: System.Address) return Boolean;

in order to have the comparison in one place only.

HTH,
 Georg 

Re: binding to C: popen

[Alex R. Mosteo]

Poul-Erik Andreasen wrote:
> jimmaureenrogers@worldnet.att.net wrote:
> 
>> Poul-Erik Andreasen wrote:
>>
>>> This ictually going as it is suppose to, but i would like set in an
>>> exception if the piping dosn't have succes. Acording to the C manual
>>> popen returns null if it fails. But how do i test on that in the 
>>> FILEs type?
>>
>>
>>
>> The popen man page describes the command as:
>> FILE *popen(const char *command, const char *mode);
>>
>> Note that popen returns a file pointer. Upon failure it returns a null
>> pointer.
>>
>> It seems that you might be able to test if the return value is null.
>>
>> Jim Rogers
>>
> 
> Yes but a C pointer is in Ada represented as system.address (...)

Not necessarily. Have a look at Interfaces.C, Interfaces.C.Pointers and 
Interfaces.C.Strings.

Also with Gnat an access type with pragma Convention (C, ...) can do the 
trick. You can easily check for null pointers that way.

Re: binding to C: popen

[Poul-Erik Andreasen]

Georg Bauhaus wrote:
> Poul-Erik Andreasen wrote:
> 
> 
>>Yes but a C pointer is in Ada represented as system.address and i can
>>not test that for O the the systems.address_image gives 0804C060 and if
>>that is a stadart c value for a null-pointer things are fine, but that
>>seems to be a hack.
> 
> 
> System.Null_Address, or Interfaces.C.Strings.Null_Ptr perhaps?
> 
> You could consider writing a predicate like
> 
>   fucntion is_null(p: System.Address) return Boolean;
> 
> in order to have the comparison in one place only.
> 
> HTH,
>  Georg 
In the meantime i have found out that i will not help much. The 
null-pointer return will only occur if there is a internal error, and 
since  sh normaly will succed even if the command fails it somthing that
rarely occurs. I can not even find out a way to test it.

Poul-Erik

Re: binding to C: popen

[Jeffrey R. Carter]

Poul-Erik Andreasen wrote:

> Yes but a C pointer is in Ada represented as system.address 

No, it's not. A C pointer in Ada is a C-convention access type. A C-convention 
access type must correspond to a C pointer. System.Address need not.

-- 
Jeff Carter
"Death awaits you all, with nasty, big, pointy teeth!"
Monty Python & the Holy Grail
20

Re: binding to C: popen

[Marc A. Criley]

Poul-Erik Andreasen wrote:
> Hi
> 
> i am trying to make a biding to the C function popen, it goes like this:

If your goal is just to get a binding to pipes, and you're less 
interested in writing it yourself, you could get Jim Roger's "pipes" 
package at 
http://www.adapower.com/index.php?Command=Class&ClassID=Bindings&CID=181

I've used this on a number of projects over the years, and it's been a 
terrific utility.

-- Marc A. Criley
-- McKae Technologies
-- www.mckae.com
-- DTraq - XPath In Ada - XML EZ Out

Re: binding to C: popen

[poulerik]

Marc A. Criley wrote:
> Poul-Erik Andreasen wrote:
> 
>> Hi
>>
>> i am trying to make a biding to the C function popen, it goes like this:
> 
> 
> If your goal is just to get a binding to pipes, and you're less 
> interested in writing it yourself, you could get Jim Roger's "pipes" 
> package at 
> http://www.adapower.com/index.php?Command=Class&ClassID=Bindings&CID=181
> 
> I've used this on a number of projects over the years, and it's been a 
> terrific utility.

Thanks , it is allways nice to see how other poeple do stuff. To answer 
your question, i have never been witing a C binding before( i am awfully 
in C), i thought i was nice litle thing to start with, and as i have 
mentioned before my binding actually works fine. Jim Rogers package dos 
either catch any errors in the opening, and as i mention elsewhere it is 
rather useles to do so.

Poul-Erik