World: r3wp

is your file a .c or .cpp  ?

.c

you can try adding 

extern  void RL_Print(char *fmt, ...);

at the begining of your file.

That does not works.

are you using gcc of VS ?

of = or

GCC

it's not working with Andreas' minimal example as well - http://www.curecode.org/rebol3/ticket.rsp?id=1727

(wrong link, this one https://gist.github.com/0c6305d7c25e40742b31
)

ah, I did a little bit of searching and I think I understand... 

try using RL_PRINT() instead.

its strange that I've never had a problem with this though cause 
I use RL_Print in all my files, but I realize that it might just 
be luck, that in my setup I don't have the linking problem you are 
having.

That works, but only with 2 args.

RL_PRINT should work in any uses of the host_kit

ok... that is easy to fix.

open reb-lib.h

and replace:
#define RL_PRINT(a,b)               RL->print(a,b)

with:
#define RL_PRINT(a,b)               RL->print(a,__VA_ARGS__)

can't test it right now, but that should work.

the function itself is defined with variable arguments, its just 
the #define which isn't ... the above redefines it so it matches 
the function declaration.

__VA_ARGS__ can only appear in the expansion of a C99 variadic macro
Never mind... I really have to do real work now :)

what?  I'm using it my own gcc compiled version of the host-kit... 
I don't understand... Andreas will have to step in... I don't know 
why you're having that error.

Actually it's:

../src/include/reb-lib.h:270:49: warning: __VA_ARGS__ can only appear 
in the expansion of a C99 variadic macro

wand.c:74:43: macro "RL_PRINT" passed 3 arguments, but takes just 
2
wand.c: In function `RX_Call':

wand.c:74: error: `RL_PRINT' undeclared (first use in this function)

ok, well, I guess you'll have to use just two args for now  ;-)

But I have a solution, this works:
RL->print("%d %s\n", n,item);

true.


btw, keep reb-lib.h open when you code extension stuff, its the best 
source to get the proper argument information for all the available 
RLxxxxx functions.

if you look at the web version it mangles the argument types, by 
stripping away any pointer use... so it gets really screwed up.

Extensions are quite additive as I'm getting closer to a real work 
:) I'm sure I will have other questions, but must force myself to 
stop now.

yes, once you understand that just about everything obeys the same 
basic pattern, it gets quite easy and addictive, since you get results 
pretty quickly  :-)

true, once I will understand the patterns, I will make a script, 
which will create the C code for me.

oh s**t, I cannot stop.. I'm already able to convert images..

hahaha

Oldes - LOL :-)

:-)

When I have integer (from REBOL side) and want to use it as a pointer, 
what I must do?

And, what would you do: (1.) Save wand pointers on REBOL side, or 
(2.) only on C side and provide just IDs (index) to this pointers 
(which is probably safer but would require dynamic array on the C 
side)?

I think I've found answer on my question, but please correct me, 
if there is better way:
            i32 magick_wand_ptr;
            MagickWand *magick_wand;
            
            magick_wand_ptr = RXA_INT32(frm, 1);
            magick_wand = magick_wand_ptr;

I think you could just do this:

magick_wand = (MagickWand*)RXA_INT32(frm, 1);

Right, that works as well:)

I§m having problems to get string from REBOL input if it's unicode:/

So with Cyphre's help I have this function:
char* rebser_to_utf8(REBSER* series) {
    char *uf8str;
    REBCHR* str;
    REBINT result = RL_GET_STRING(series, 0 , (void**)&str);
        
    if (result > 0){
        //unicode string
        int iLen = wcslen(str);
        int oLen = iLen *  sizeof(REBCHR);
        uf8str = malloc(oLen);

        int result = WideCharToMultiByte(CP_UTF8, 0, str, iLen, uf8str, oLen, 
        0, 0);
        if (result == 0) {
            int err = GetLastError();
            RL->print("err: %d\n", err);
        }
    } else if (result < 0) {
        //bytes string (ascii or latin-1)
        uf8str = malloc(strlen((char *)str));
        strcpy(uf8str, (char *)str);
    }
    return uf8str;
}

and I can than use:
..
            char *filename = rebser_to_utf8(RXA_SERIES(frm, 1));
            status=MagickReadImage(current_wand, filename);
            free(filename);
            if (status == MagickFalse) {
                ThrowWandException(current_wand);
            }
            return RXR_TRUE;

Is it correct? It's working but maybe there is something I don't 
see as a C newbie.

Why are you using an integer on the REBOL side to store a pointer? 
That is what handle! is for.

because I don't know handle. I'm learning and there are no examples 
yet

REBOL doesn't have pointers, it has references, and it doesn't have 
addresses. So the only way you could legitimately get a pointer is 
to return it from a command. But you don't want to have any way to 
construct an illegitimate pointer in REBOL and pass it to a command 
because that would be a much worse security and stability problem 
than just having commands at all, and treating pointers as integers 
lets you do that. So there is the handle! type to store pointers. 
A handle! is an immediate value that is the size of a pointer, but 
that you can't convert directly to or from any other value, or even 
mold it to see its contents. When you return a pointer from a command 
you set the value to the handle! type. Then that handle! will be 
usable when passed back to other commands in the same extension, 
and maybe even when passed to other extensions, depending on address 
space issues. Handles are also used to store function pointers in 
R3, and other opaque system values like library addresses.

changed to use handle, but the string conversion function is probably 
bad.

What you absolutely don't want to have available in REBOL code is 
address arithmetic. That should be reserved for native code.

Right, now it's clear that I cannot mess with the wand pointers, 
so it's safe to store the wands on the REBOL side. Thanks for that 
info.

And on that subject, what is the current state of string conversion 
in extensions? When last I checked it was really poor, all sorts 
of missing macros.

Oldes: HAve you tested the function with a string including a unicode 
code point which translates to a three-byte utf-8 character? The 
size of utf8str appears to beonly  twice the number of codepoints 
in the REBOL stirng.


A good example of a three-byte utf-8 character is the Euro sign - 
Unicode 20AC UTF-8 E2 82 AC

Right, so what is the best way to allocate the buffer. Also the function 
as it is is working strange if I use it multiple times. So I guess 
the allocation is bad.

The maximum length of a utf-8 translation of a UCS-2 string would 
be 1.5 times the length of the string. So if wcslen returns the number 
of codepoints in a string, the length of the utf-8 should be the 
length of the str multiplied by 3 integer divided by 2 plus 1.

If wcslen returns the length in bytes then multiply it by 3.