Re: Interfaces.C.Strings

[Jeffrey Carter <jrcarter@acm.org>]

Philippe Tarroux wrote:
> 
> This function returns a Chars_Ptr (Char *) type which is a pointer to a
> char_array supposed to be nul terminated. In the present case, this array
> contains pixel values and probably several nul values. The array I get from
> the Interfaces.C.Strings.Value procedure is truncated to the first nul and I
> was unable to find a way to bypass this limitation.

The main problem here is that "char*" means a lot of different things in
C, and some of them have nothing to do with characters or strings. This
function is an example of that. The return value is a pointer to an
array of what are referred to in Ada as Storage_Elements (type
System.Storage_Elements.Storage_Element), usually bytes, not to a
NUL-terminated string. Thus, using Value is probably inappropriate,
although a version of Value that takes a Length parameter may do what
you want.

In general, though, you might want to define a C-convention access type
designating System.Storage_Elements.Storage_Array (or even better a
suitably constrained subtype) and import a function returning that
access type.

-- 
Jeff Carter
"Nobody expects the Spanish Inquisition!"
Monty Python's Flying Circus