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From: Freddy <Alfred.Hilscher@t-online.de>
Newsgroups: comp.lang.ada
Subject: Re: Exceptions vs Error return values
Date: Mon, 06 Aug 2001 23:31:41 +0200
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Date: 2001-08-06T23:31:41+02:00
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Hambut schrieb:
> 
> I'm currently trying to get to grips with winsock programming.  As
> part of this process I'm trying to put together a slightly higher
> level binding to the thin one provided with Gnat.
> 
> The 'thin' binding provides a lot of functions returning an
> integer. The value of this integer encodes a whole range of possible
> errors.  I want to replace this 'C'-esque way of doing stuff with Ada
> exceptions; my question is "What is a sensible guideline for choosing
> between exceptions and error return codes?"

In my own bindings (a port from Modula-2) I prefered return values as 
 - it is more effectiv
 - it prevents the programmer from writing a lot of exception handlers
(for nearly every call), you would have to
   catch (and handle) all IP related exception (you shouldn't use the
"others" choice)
 - it's more readable
 - it is sometimes not relevant what the actual returncode was (some of
the codes are not really exceptual)

This is my personal preference, others may differ.


  procedure Ping (Host : STRING; RC : out Integer) is
    s : Socket;
    Result : Integer;
    Data : STRING := "        abcdef";
    Buffer : STRING (1..255);
    Buffer_Len : Integer;
    Host_IP : IPV4;
    Sender : IPV4;
    Sender_Port : Integer;
  begin
    RC := No_Error;
    
    Init (Result);
    if Result /= No_Error then RC := Result; return; end if;

    GetHostAddress (Host, Host_IP, Result);
    if Result /= No_Error then RC := Result; Cleanup (Result); return;
end if;

    CreateRawSocket (Protocoll_ICMP, s, Result);
    if Result /= No_Error then RC := Result; Cleanup (Result); return;
end if;
  
    Fill_Header (1, 1, Data);
    
    SendTo (s, Data, Host_IP, 0, RC, Timeout_Immediate);    
    if Result /= No_Error then RC := Result; Cleanup (Result); return;
end if;

    RecvFrom (s, Buffer, Buffer_Len, Sender, Sender_Port,  Result,
1000);    
    if Result /= No_Error then RC := Result; Cleanup (Result); return;
end if;
    
    Cleanup (Result);  
    if Result /= No_Error then RC := Result; end if;
  end Ping;