Re: Passing a String to a C/C++ Subprogram (Special Case)

[Shark8 <onewingedshark@gmail.com>]

On Tuesday, October 15, 2013 3:13:09 PM UTC-6, Eryndlia Mavourneen wrote:
> On Tuesday, October 15, 2013 3:59:21 PM UTC-5, Jeffrey Carter wrote:
> 
> > On 10/15/2013 12:54 PM, Eryndlia Mavourneen wrote:
> 
> > 
> 
> > >  . . .
> 
> > 
> 
> > If I were doing this, I would wrap each in an Ada subprogram that ensures the 
> 
> > String will be passed correctly to C. Ultimately it will be less effort.
> 
> > 
> 
> 
> 
> Thanks, Jeff.  This could be a good way to manage things.  Unfortunately, I can not guarantee that I can perform a trim operation or that the last character is indeed not being used (for the placement of a nul).  I suppose I could create the wrapper, as you said, and copy the String (1 .. size) to a String (1 .. size + 1) and place a nul in the last character of the target string.  Of course, this does not add a lot of overhead for short strings, but it is a hard real-time system.
> 
> 
> 
> It sounds as if I need to get with my people and get a further, clear consensus about how this stuff is going to be used, in reality.
> 
> 
> 
> -- Eryndlia Mavourneen (KK1T)

Could you use an Ada 2012 subtype predicate? something like:

    Type Transport_String is array (1..31) of Character
        with Default_Component_Value => ASCII.NUL,
        Dynamic_Predicate => Transport_String(Transport_String'Last) = ASCII.NUL;

Actually I'm rather disappointed that there aren't static_predicates available for Arrays. I had hoped to, in my OpenGL binding, have something like the following available for the vector operations:

    Type RGBA is (Red, Blue, Green, Alpha); 
    Subtype RGB is RGBA range Red..Blue;
    
    --  Declare the general Vector-type for OprnGL which has vectors
    --  of three or four components of RGBA [A being optional], always
    --  starting with R.
    Type Float_Vector is array(RGBA range <>) of Float
        with Static_Predicate => Float_Vector'First = Red;