[REBOL] Re: External library interface
From: nitsch-lists:netcologne at: 2-Jul-2003 22:11
Am Mittwoch, 2. Juli 2003 15:12 schrieb Ladislav Mecir:
> Hi all,
>
> I tried to help Cyphre with a specific problem (OpenGL 3D). I found a
> following problem in the interface between Rebol strings and external
> strings.
>
> First I try to make a C string usable for an external function:
>
> rebol_string: "12^(0)4"
> c_string: third make struct! [s [string!]] reduce [rebol_string]
>
> So far so good, I created a binary! data (in fact a pointer), that can be
> passed to a library function as a C string.
>
> Now let's suppose, that a library function returns a C string. How can this
> be done? One possibility is to store such a pointer into a Rebol integer.
> Not having Rebol/Command, I cannot call a library function now, but I can
> "simulate" this situation using the C string I prepared above. To do it, I
> just convert the above C string to a Rebol integer.
>
> integer_struct: make struct! [i [integer!]] none
> change third integer_struct c_string
> rebol_integer: integer_struct/i
>
> Now I obtained the C string as an integer and I can pretend, that it is a
> result of an external library function. What to do with it to obtain a
> Rebol string? Let's try to use a similar "trick" as above:
>
> result_integer_struct: make struct! [i [integer!]] reduce
> [rebol_integer] result_string_struct: make struct! [s [string!]] none
> change third result_string_struct third result_integer_struct
> result_string: result_string_struct/s ; == "12"
>
> Now the problem: as we have seen, the RESULT_STRING_STRUCT doesn't know the
> length of the string (as usual for C strings) and therefore it assumes,
> that the string is a null-terminated string as usual in C, so it "leaves
> off" a part of the string. While this is reasonable for strings, I doubt,
> it is reasonable for binary data, like images.
>
> Do you have any idea how to handle binary data or strings containing null
> characters?
Write a wrapper-function in c.
call the wrapper-function with a buffer.
copy the result in the buffer.
> -L
-V
