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

[Georg Bauhaus <rm.dash-bauhaus@futureapps.de>]

On 15.10.13 23:13, Eryndlia Mavourneen wrote:
> 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).

There is, in addition, a logical bridge between the languages
in addition to the technical one:

C programmers who know the "strn..." functions of C's standard
C library will not be surprised to see a subprogram profile
involving a string that has both a char* and a size_t. (In fact,
this way of handling string data is sometimes recommended.) Then,

   type My_Size_T is mod 2**Positive'Size;

   procedure C_Prog (C_String : in String;
                     C_Size_T : in My_Size_T);

where My_Size_T reflects String's index type. It might be a slightly
more reliable approximation to what you'd write with Interfaces.*.
and Conventions applied to the types, especially in corner cases
when the string is empty, or if all components allocated are used
so that there is no room for storing a terminating '\0' in C.

There can be concerns about size_t being too different from My_Size_T
just like char'Size and Character'Size might differ. (E.g. Janus/Ada
reportedly has Positive'Size = 16 while the C compiler's size_t may
require more than 16 bits.) Sizes can be checked at compile time.