Re: Ada array vs C pointer (call by reference)

["Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org>]

Adrian Hoe wrote:
> 
>    int pwmRead (int pwmCount, float * data);
> 
> where data is an array of float which size is determined by pwmCount.
> 
> In Ada, I have:
> 
>    PWM_Count : Integer := No_Of_Components_Intended;
>    PWM_Data : array (1 .. PWM_Count) of Float;
> 
> My concern is how safe to pass an Ada array to a C function as a
> pointer (call by reference)? I presume Ada will allocate contiguous
> memory for array, but what if it does not? How can we establish a
> deterministic allocation and to make sure float * is accessed
> contiguously? Is there any "safe" way to do this?

type C_Data is array (Positive range <>) of Interfaces.C.C_Float;
pragma Convention (C, C_Data);

function PWM_Read  (Count : in Interfaces.C.Int; Data : in C_Data)
return Interfaces.C.Int;
pragma Import (C, PWM_Read, "pwmRead");

PWM_Count : constant := ...;

PWM_Data : C_Data (1 .. PWM_Count);
Result   : Interfaces.C.Int;

Result := PWM_Read (PWM_Count, PWM_Data);

-- 
Jeff Carter
"Your mother was a hamster and your father smelt of elderberries."
Monty Python & the Holy Grail
06