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From: "Alex R. Mosteo" <devnull@mailinator.com>
Newsgroups: comp.lang.ada
Subject: Re: binding to C: popen
Date: Tue, 21 Feb 2006 17:12:04 +0100
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Date: 2006-02-21T17:12:04+01:00
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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.