Re: [AL] help understanding a few things

[William F B L. <zh...@nt...>]

thanks

----- Original Message -----
From: "Neil Roy" <ne...@co...>
To: <all...@li...>
Sent: Sunday, July 27, 2003 10:24 PM
Subject: Re: [AL] help understanding a few things


> William F B Labbett wrote:
>
> > hi again,
> >
> >  i really want to understand this
> > file (attached) which Marcel
> > wrote to help me do something
> > as i think i could learn a fair bit from it. The trouble is i've
> > never learnt any C++ and am reluctant to do so until
> > i feel better about programming in C.
> >  Marcel has said there's only
> > a little C++ in it so i should be okay if i try a little harder.
>
> The C++ portions of that code is where he defines the variables in the
> middle of the code, this is about the only thing I don't like about C++,
> I think it is messy and variables should be defined at the beginning of
> a function.
> I am no expert on C++ but I am wondering if it is even okay to define a
> constant variable in the middle of a loop like that?
>
> >  I don't understand the contents of the for loop.
> > For instance where are things like getb etc deifined?
>
> getb() is an allegro function, it gets the blue component of an RGB
> value (the pixel colour he read from Source was stored in CS and then
> getb() was used to extract how much BLUE was in that pixel).
>
> > Also, i'd like to understand what the first define does;
> >
> > #define ALLEGRO_USE_CONSOLE
>
> Probably tells Allegro that you will be using the console as opposed to
> windows.  (console mode = dos text mode)
>
> >  i've only ever used defines for defining
> > constant values.
>
> It is simply defining that label really, with no value.  Allegro will
> check to see if if has been defined something like this...
>
> #ifdef ALLEGRO_USE_CONSOLE
> //do stuff here if it is defined
> #endif
>
> But remember, #defines aren't really C/C++ code but rather compiler
> directives.  When you use something like #include you are telling the
> COMPILER to include that files contents at the beginning of the current
> file you are working on.  When you #define it is similar, the compiler
> checks to see if ALLEGRO_USE_CONSOLE is defined in that above #ifdef and
> if it is, it will compile the code in between #ifdef and #endif.  If it
> isn't defined than that code will not be compiled at all and never be
> part of the final executable.
>
>
> --
> Neil Roy - http://home.cogeco.ca/~nroy15
>
> "My religion consists of a humble admiration of the illimitable superior
> spirit who reveals himself in the slight details we are able to perceive
> with our frail and feeble mind." - Albert Einstein
>
>
>
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