Interfaces.C.Strings

Interfaces.C.Strings

[Philippe Tarroux]

I got a problem in interfacing a TclTk function with Ada:

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.

I came to the conclusion that there is no way in Ada to get an array pointed
by a Chars_Ptr  and containing nul values?

Am I wrong?

Re: Interfaces.C.Strings

[sk]

Hi,

Firstly, have you looked at the GtkAda stuff ?

If this still doesn't meet your needs, you 
might try "re-modeling" the arrays of pixel
values and try using the techniques described
in the previous c.l.a thread,

"C lib returns char** - How in ADA?"

The "re-modeling" is that you are not really
pointing to an array of null terminated
strings, you are pointing to an array of
something else so don't try to pretend that
they are strings.

-- 
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Re: Interfaces.C.Strings

[Jeffrey Carter]

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