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NNTP-Posting-Date: Sat, 14 Aug 2010 05:49:41 -0500
From: Brian Drummond <brian_drummond@btconnect.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada Smileys in C++ lib Conversion
Date: Sat, 14 Aug 2010 11:57:07 +0100
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Date: 2010-08-14T11:57:07+01:00
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On Fri, 13 Aug 2010 18:36:38 -0700 (PDT), Warren <ve3wwg@gmail.com> wrote:

>On Aug 13, 12:53�pm, Anh Vo <anhvofrc...@gmail.com> wrote:
>> On Aug 13, 7:20�am, Warren <ve3...@gmail.com> wrote:

#define MC_CTL_LOCAL_C  0x80 // Local on/off
#define MC_CTL_ALLN_OFF 0x81 // All notes off

>> > it immediately identified the value MC_CTL_LOCAL_C
>> > (and others) as not fitting into the Control_Type's
>> > valid range. In C++ a glaring error had gone
>> > unnoticed:

>> I am smiling, too, since I am not surprised at all. 

>Heh heh. This is one of those things that C/C++ cannot
>guard against at all. Unless the value(s) were to exceed
>the underlying type's storage capability, the compiler
>is helpless to identify it. There is simply no concept of
>a "range" of valid values in that language.
>
>About the only thing you could do (in C/C++) is to code
>a macro check on the constants, but I don't think I've
>ever seen it done in practice.  Only as a argument value
>assertion check in strategic places.

Heh too.

I thought I was being really really smart years ago in C, when I decided to
convert all those #defines to integer constants...

const int MC_CTL_LOCAL_C  = 0x80;
and so on.

Of course I was declaring integer variables, who's storage class happens to be
named "constant".

But it certainly puzzled me to be told that I couldn't use a "const" in a
constant expression!

- Brian