Pointer

Pointer

[Sébastien]

Hi,

I'm getting from a C interfaces a char**data in a System.Address. I have 
the following hypothesis:
- data is an array of n elements where n is known
- There is no memory issue (meaning data[i] with i < n is allocated)
- I do not have to free the memory (memory is managed by the C library)

How can I retrieve all my values in the C arrays using a loop to create 
some Ada String (Interfaces.C.Strings.Value)?

thanks by advance,
Sebastien

Re: Pointer

[Dmitry A. Kazakov]

On Mon, 19 May 2008 09:38:08 +0000, S�bastien wrote:

> I'm getting from a C interfaces a char**data in a System.Address. I have 
> the following hypothesis:
> - data is an array of n elements where n is known
> - There is no memory issue (meaning data[i] with i < n is allocated)
> - I do not have to free the memory (memory is managed by the C library)
> 
> How can I retrieve all my values in the C arrays using a loop to create 
> some Ada String (Interfaces.C.Strings.Value)?

Suggesting, n is returned from the C program:

with Interfaces.C;  use Interfaces.C;
with Interfaces.C.Strings;  use Interfaces.C.Strings;

function Get_It return String is
   procedure Internal (N : out size_t; Data : out chars_ptr);
   pragma Import (C, Internal, "<C-name>");
   Data : chars_ptr;
   N : size_t;
begin
   Internal (Data);
   return Value (N, Data);
end Get_It;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Pointer

[Dmitry A. Kazakov]

On Mon, 19 May 2008 11:53:11 +0200, Dmitry A. Kazakov wrote:

> On Mon, 19 May 2008 09:38:08 +0000, S�bastien wrote:
> 
>> I'm getting from a C interfaces a char**data in a System.Address. I have 
>> the following hypothesis:
>> - data is an array of n elements where n is known
>> - There is no memory issue (meaning data[i] with i < n is allocated)
>> - I do not have to free the memory (memory is managed by the C library)
>> 
>> How can I retrieve all my values in the C arrays using a loop to create 
>> some Ada String (Interfaces.C.Strings.Value)?
> 
> Suggesting, n is returned from the C program:
> 
> with Interfaces.C;  use Interfaces.C;
> with Interfaces.C.Strings;  use Interfaces.C.Strings;
> 
> function Get_It return String is
>    procedure Internal (N : out size_t; Data : out chars_ptr);
>    pragma Import (C, Internal, "<C-name>");
>    Data : chars_ptr;
>    N : size_t;
> begin
>    Internal (Data);

Internal (N, Data);  -- Of course

>    return Value (N, Data);
> end Get_It;


-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Pointer

[Sébastien]

> Suggesting, n is returned from the C program:
> 
> with Interfaces.C;  use Interfaces.C;
> with Interfaces.C.Strings;  use Interfaces.C.Strings;
> 
> function Get_It return String is
>    procedure Internal (N : out size_t; Data : out chars_ptr);
>    pragma Import (C, Internal, "<C-name>");
>    Data : chars_ptr;
>    N : size_t;
> begin
>    Internal (Data);
>    return Value (N, Data);
> end Get_It;

Yes it's exaclty what I did ... and it's exaclty what I would like to 
avoid :-) Actually, I was looking for a pure Ada solution.
I think there is a way using an unchecked type conversion, but how to be 
sure of the size of the System.Address?

Re: Pointer

[Dmitry A. Kazakov]

On Mon, 19 May 2008 10:13:48 +0000, S�bastien wrote:

>> Suggesting, n is returned from the C program:
>> 
>> with Interfaces.C;  use Interfaces.C;
>> with Interfaces.C.Strings;  use Interfaces.C.Strings;
>> 
>> function Get_It return String is
>>    procedure Internal (N : out size_t; Data : out chars_ptr);
>>    pragma Import (C, Internal, "<C-name>");
>>    Data : chars_ptr;
>>    N : size_t;
>> begin
>>    Internal (Data);
>>    return Value (N, Data);
>> end Get_It;
> 
> Yes it's exaclty what I did ... and it's exaclty what I would like to 
> avoid :-) Actually, I was looking for a pure Ada solution.

In what sense pure? Do you want to re-implement Interfaces.C.String?

> I think there is a way using an unchecked type conversion, but how to be 
> sure of the size of the System.Address?

(And how to sure about the size of Character vs. char?)

You could convert System.Address to a pointer of an Ada object using an
instance of System.Address_To_Access_Conversions.

(It seems that I don't fully understand your problem)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Pointer

[Ludovic Brenta]

Sébastien wrote:
> > Suggesting, n is returned from the C program:
> >
> > with Interfaces.C;  use Interfaces.C;
> > with Interfaces.C.Strings;  use Interfaces.C.Strings;
> >
> > function Get_It return String is
> >    procedure Internal (N : out size_t; Data : out chars_ptr);
> >    pragma Import (C, Internal, "<C-name>");
> >    Data : chars_ptr;
> >    N : size_t;
> > begin
> >    Internal (Data);
> >    return Value (N, Data);
> > end Get_It;
>
> Yes it's exaclty what I did ... and it's exaclty what I would like to
> avoid :-) Actually, I was looking for a pure Ada solution.
> I think there is a way using an unchecked type conversion, but how to be
> sure of the size of the System.Address?

procedure To_String (Pointer : in System.Address; Length : in Natural)
return String is
   Result : String (1 .. Length);
   for Result'Address use Pointer;
   pragma Import (Ada, Result); -- suppress default initialization
begin
   return Result;
end To_String;

But Dmitryi's solution is safer, of course. HTH

--
Ludovic Brenta.

Re: Pointer

[Sébastien]

> procedure To_String (Pointer : in System.Address; Length : in Natural)
> return String is
>    Result : String (1 .. Length);
>    for Result'Address use Pointer;
>    pragma Import (Ada, Result); -- suppress default initialization
> begin
>    return Result;
> end To_String;
> 
> But Dmitryi's solution is safer, of course. HTH

Ok, I was not clear enough. Converting char* to String is not an issue, 
I'm using Interfaces.C.String with no problem. My problem is to convert 
all the strings in the char** in string one by one.

Something like this:
CharPtrPtr: System.Address := MyCFunctionReturninCharStarStar;
N: Natural := MYCFunctionTellingMeHowManyStrings;

for i in Natural range 0 .. N loop
    -- Some ada code to convert CharPtrPtr[i] to String
end loop;

Of course I can do somthing like that:

Compile this using
gcc -O2 -g3 -ansi -pedantic -W -Wall -c mybind.c -o mybind.o:

char* get_nth(char** data, unsigned int n) {
   return data[i];
}

Ada binding:
function get_nth(data: System.Address; n: Int) return Char_Ptr;
pragma Import(C, get_nth, "get_nth");

Then:
for i in Natural range 0 .. N loop
    MyString := Interfaces.C.Strings.Value(get_nth(CharPtrPtr, i));
end loop;

I know it's working, but I have to code a C function in order to do 
that, is there a way to replace get_nth by an ada code function?

Hope it's a better explanation ;-)

Re: Pointer

[Ludovic Brenta]

Sébastien wrote:
> char* get_nth(char** data, unsigned int n) {
>    return data[i];
> }
>
> Ada binding:
> function get_nth(data: System.Address; n: Int) return Char_Ptr;
> pragma Import(C, get_nth, "get_nth");
>
> Then:
> for i in Natural range 0 .. N loop
>     MyString := Interfaces.C.Strings.Value(get_nth(CharPtrPtr, i));
> end loop;
>
> I know it's working, but I have to code a C function in order to do
> that, is there a way to replace get_nth by an ada code function?
>
> Hope it's a better explanation ;-)

OK, then how about:

type Array_Of_C_Strings is array (Positive range <>) of
Interfaces.C.Strings.chars_ptr;
pragma Convention (C, Array_Of_C_Strings);

type Array_Of_Strings is array (Positive range <>) of access String;

function Get return Array_Of_C_Strings is
   function How_Many_Strings return Natural;
   pragma Import (C, How_Many_Strings,
"MYCFunctionTellingMeHowManyStrings");
   Length : constant Natural := How_Many_Strings;

   function Get_Array return Array_Of_C_Strings;
   pragma Import (C, Get_Array, "MyCFunctionReturninCharStarStar");

   Raw_Result : Array_Of_C_Strings (1 .. Length) := Get_Array;
   Result : Array_Of_Strings (1 .. Length);
begin
   for K in Result'Length loop
      Result (K) := new String'(Interfaces.C.Strings.Value (Raw_Result
(K)));
   end loop;
   return Result;
end Get;

This duplicates the strings and creates an array of access values;
each access value remembers the length of the string it points to.
There is probably another solution that avoids this duplication.

--
Ludovic Brenta.

Re: Pointer

[Dmitry A. Kazakov]

On Mon, 19 May 2008 11:31:57 +0000, S�bastien wrote:

>> procedure To_String (Pointer : in System.Address; Length : in Natural)
>> return String is
>>    Result : String (1 .. Length);
>>    for Result'Address use Pointer;
>>    pragma Import (Ada, Result); -- suppress default initialization
>> begin
>>    return Result;
>> end To_String;
>> 
>> But Dmitryi's solution is safer, of course. HTH
> 
> Ok, I was not clear enough. Converting char* to String is not an issue, 
> I'm using Interfaces.C.String with no problem. My problem is to convert 
> all the strings in the char** in string one by one.

Aha, it is const char *[] ...

> Something like this:
> CharPtrPtr: System.Address := MyCFunctionReturninCharStarStar;
> N: Natural := MYCFunctionTellingMeHowManyStrings;
> 
> for i in Natural range 0 .. N loop
>     -- Some ada code to convert CharPtrPtr[i] to String
> end loop;

with Interfaces.C.Pointers;
with Interfaces.C.Strings;  use Interfaces.C.Strings;
with Interfaces.C; use Interfaces.C;

type Chars_Ptr_Array is array (size_t range <>) of aliased chars_ptr;
pragma Convention (C, Chars_Ptr_Array);
package Pointers_To_String is
   new Interfaces.C.Pointers (size_t, chars_ptr, chars_ptr_array, null);
use Pointers_To_String;
...   
Data : Pointers_To_String.Pointer := MyCFunctionReturninCharStarStar;
N: Natural := MYCFunctionTellingMeHowManyStrings;
...
for Index in 1..N loop
   declare
      Element : String := Value (Data.all);
   begin
      ... -- Use the element
   end;
   Increment (Data); -- Move to the next one
end loop;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Pointer

[Sébastien]

> with Interfaces.C.Pointers;
> with Interfaces.C.Strings;  use Interfaces.C.Strings;
> with Interfaces.C; use Interfaces.C;
> 
> type Chars_Ptr_Array is array (size_t range <>) of aliased chars_ptr;
> pragma Convention (C, Chars_Ptr_Array);
> package Pointers_To_String is
>    new Interfaces.C.Pointers (size_t, chars_ptr, chars_ptr_array, null);
> use Pointers_To_String;
> ...   
> Data : Pointers_To_String.Pointer := MyCFunctionReturninCharStarStar;
> N: Natural := MYCFunctionTellingMeHowManyStrings;
> ...
> for Index in 1..N loop
>    declare
>       Element : String := Value (Data.all);
>    begin
>       ... -- Use the element
>    end;
>    Increment (Data); -- Move to the next one
> end loop;

Ok I didn't know Interfaces.C.Pointer, it's looks like exaclty what I 
need and it's a replacement for pointer arithmetic operations.

Re: Pointer

[Matthew Heaney]

On May 19, 7:31 am, Sébastien <seb.mor...@gmail.com> wrote:
>
> I know it's working, but I have to code a C function in order to do
> that, is there a way to replace get_nth by an ada code function?

No, you don't need a function written in C.  Just use an address
clause, as I described in my original post.

Re: Pointer

[Matthew Heaney]

On May 19, 6:13 am, Sébastien <seb.mor...@gmail.com> wrote:
>
> Yes it's exaclty what I did ... and it's exaclty what I would like to
> avoid :-) Actually, I was looking for a pure Ada solution.
> I think there is a way using an unchecked type conversion, but how to be
> sure of the size of the System.Address?

If you don't want to use an address clause, you could do something
like:

procedure Op (argv_Address : System.Address) is
   type Argv_Type is array (Positive) of chars_ptr;
   pragma Convention (C, Argv_Type);

   type Argv_Pointer is access all Argv_Type;
   for Argv_Pointer'Storage_Size use 0;
   pragma Convention (C, Argv_Pointer);

   function To_Argv_Pointer is
     new Unchecked_Conversion (System.Address, Argv_Pointer);

   Argv : constant Argv_Pointer :=
     To_Argv_Pointer (argv_Address);

begin
   -- same as in my last post
end;

Re: Pointer

[Matthew Heaney]

On May 19, 5:38 am, Sébastien <seb.mor...@gmail.com> wrote:
>
> I'm getting from a C interfaces a char**data in a System.Address. I have
> the following hypothesis:
> - data is an array of n elements where n is known
> - There is no memory issue (meaning data[i] with i < n is allocated)
> - I do not have to free the memory (memory is managed by the C library)
>
> How can I retrieve all my values in the C arrays using a loop to create
> some Ada String (Interfaces.C.Strings.Value)?

procedure Op (argv_Address : System.Address; N : Natural) is
   type Argv_Type is array (Positive) of chars_ptr;
   pragma Convention (C, Argv_Type);

   Argv : Argv_Type;
   for Argv'Address use argv_Address;

begin
   for I in 1 .. N loop
      Put_Line (Value (Argv (I)));  -- or whatever
   end loop;
end Op;

Is that what you had in mind?

Re: Pointer

[Sébastien]

> procedure Op (argv_Address : System.Address; N : Natural) is
>    type Argv_Type is array (Positive) of chars_ptr;
>    pragma Convention (C, Argv_Type);
> 
>    Argv : Argv_Type;
>    for Argv'Address use argv_Address;
> 
> begin
>    for I in 1 .. N loop
>       Put_Line (Value (Argv (I)));  -- or whatever
>    end loop;
> end Op;
> 
> Is that what you had in mind?

Yes, thanks very much for all the codes you provided, it helps me a lot 
to understand all aspects of the problem.

Sebastien

pointer

[TC]

How translate this c code?

typedef struct
{
	unsigned char sParola [50];
	int iFrequenza;
}Parola;


struct Lista
{
	Parola P;
	struct Lista *next;
};


struct Lista *vett[26];


struct Lista *LF;

please help me!

Re: pointer

[Martin Krischik]

TC wrote:

> How translate this c code?
> 
> typedef struct
> {
> unsigned char sParola [50];
> int iFrequenza;
> }Parola;
> 
> 
> struct Lista
> {
> Parola P;
> struct Lista *next;
> };
> 
> 
> struct Lista *vett[26];
> 
> 
> struct Lista *LF;
> 
> please help me!

you will need:

Strings: http://en.wikibooks.org/wiki/Ada_Programming/Strings
Records: http://en.wikibooks.org/wiki/Ada_Programming/Types/record
Access Types: http://en.wikibooks.org/wiki/Ada_Programming/Types/access
Arrays: http://en.wikibooks.org/wiki/Ada_Programming/Types/array

Martin

-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com

Re: pointer

[Jeffrey Carter]

TC wrote:
> How translate this c code?

It depends on what you mean by "translate". One could write C-in-Ada 
that would be just like this, with all the opportunities for error that 
implies.

However, it looks as if you're implementing a linked list with a record 
as its data. To do that it's probably best to use the list component of 
the standard data-structure library that will be part of Ada 0X. If you 
can't do that, because you don't have an Ada-0X compiler, you can find 
list components in most of the many fine Ada data-structure libraries 
that are available on the web. I recommend the PragmAda Reusable 
Components, but I may be biased.

Looking more closely, this appears to be part of a word-counting 
program, and so probably homework. If you're doing word counting, you 
probably want something that allows O(log N) (or better) insertions and 
lookup, such as a map component from Ada.Containers (Ada 0X), or the 
skip list from the PragmARCs.

-- 
Jeffrey Carter
"Now go away or I shall taunt you a second time."
Monty Python and the Holy Grail
E-mail: jeffrey_r_carter-nr [commercial-at]
         raytheon [period | full stop] com