Re: Using Posix with Apex

[mheaney@ni.net (Matthew Heaney)]

In article <32ee8e2c.1005715@NEWS.CLOUD9.NET>, pvanbell@cloud9.net (Paul
Van Bellinghen) wrote:


>Output_File_Name.Name :=
>           Posix.To_String (Posix.Value
>           (Posix_Process_Environment.Argument_List, 2));

If you don't know the length of the string returned by a function, then in
Ada 83 just declare the object as a constant in some dynamic scope:

declare
   The_Name : constant POSIX_String :=
      POSIX.Value (POSIX_Process_Environment.Argument_List, 2);
begin
   Output_File_Name.Name (1 .. The_Name'Length) :=
       POSIX.To_String (The_Name);
end;

>however, I kept getting an "invalid argument" exception when the code
>was executed. I called the  Rational support team and found out that
>the line suld read
>
>        Output_File_Name.Name
>           (1 .. Posix.To_String
>           (Posix.Value (Posix_Process_Environment.Argument_List, 2))'
>                 Length) :=
>           Posix.To_String (Posix.Value
>           (Posix_Process_Environment.Argument_List, 2));

Rational gave you some bad advice.  Please don't write code like this:
you're calling the function twice, and it's completely unreadable.  This is
not an Ada "problem."

Use declare blocks to hold intermediate values, especially for the result
of a function that returns an unconstrained array.  (Just remember: in Ada
83 you have to declare the object as a constant; this rule went away in Ada
95.)

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Matthew Heaney
Software Development Consultant
<mailto:matthew_heaney@acm.org>
(818) 985-1271