Re: Interfacing to C

[Keith Thompson <kst-u@mib.org>]

"Hibou57 (Yannick Duchêne)" <yannick_duchene@yahoo.fr> writes:
> On 24 déc, 10:46, "RasikaSriniva...@gmail.com"
> <rasikasriniva...@gmail.com> wrote:
>> I am building an interface to a C library. This library uses structs
>> like the following:
>>
>> typedef struct {
>>     x : int ;
>>     y : int }  MyStruct ....

(The correct syntax is:
    typedef struct {
        int x;
        int y;
    } MyStruct;
)

>> While passing variables of this type to functions, the convention in C
>> is to pass by value (best of my knowledge).

Yes.  In fact, C doesn't have pass by reference as a language feature;
*all* function arguments are passed by value.

For structs, it's very common in C to do the equivalent of
pass-by-reference, by explicitly passing the address of the struct
object.  This is partly because very old versions of C didn't
support struct parameters.

I find it a bit odd that Ada imposes a pass-by-pointer convention for
C structs.

(No, C arrays aren't passed by reference.  C array expressions, in
most contexts, are implicitly converted to pointers; the resulting
pointer can be passed by value.)

[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"