string as message argument in c object

    José López-Montes
    Jul 09 2013 | 5:36 pm
    Hi everybody,
    I´m VERY newbie to C and to creating externals. I need to pass a string as a messages argument. In this external, when I send the message ' getText "a simple string" ' the method getText must send exactly the same string to the Max window. I only get weird symbols (always different ones in every max session). The external code is in the attachment.
    I suppose this a very simple question (related maybe to proxies), but I'm blocked here after readings tutorials and forum threads. Thanks in advance for your help.
    José López-Montes
    • Luigi Castelli
      Jul 09 2013 | 7:00 pm
      Hi there,
      you need to declare your t_symbol as a pointer. Here is your corrected code: ` ////////////////////////// object struct typedef struct _genomus { t_object s_obj; long s_value; t_symbol *x_getText; long m_outlet; void *s_proxy; } t_genomus;
      ///////////////////////// function prototypes //// standard set void *genomus_new(t_symbol *s, long argc, t_atom *argv); void genomus_getText(t_genomus *x, t_symbol *getText);
      t_class *s_genomus_class;
      int main() { post("GenoMus - test version\n"); t_class *c; c = class_new("genomus", (method)genomus_new, (method)NULL, sizeof(t_genomus), 0L, 0); class_addmethod(c, (method)genomus_getText, "getText", A_SYM, 0); class_register(CLASS_BOX, c); s_genomus_class = c; return 0; }
      void *genomus_new() { t_genomus *x = (t_genomus *)object_alloc(s_genomus_class); x->s_proxy = proxy_new((t_object *)x, 1, &x->s_value); x->m_outlet = outlet_new((t_object *)x, NULL); x->x_getText = NULL; return x; }
      void genomus_getText(t_genomus *x, t_symbol *getText) { post("received string: %s", getText->s_name); } `
      You might also carefully study the code examples that come with the SDK. They show a number of useful techniques that you can use in various contexts.
      Let me know if the above code works as you want because I just made the corrections without testing the new code.
      Best
      - Luigi
    • Peter Castine
      Jul 09 2013 | 7:05 pm
      You have to understand the difference between Max symbols and C strings.
      Max symbols are pointers to a data structure that, among other things, contains a pointer to the C string that is associated with the symbol.
      Try this:
      ` void genomus_getText(t_genomus *x, t_symbol getText) { post("received string: %s\n", getText->s_name); } `
      For production code you will need to add safety checks (make sure that getText is not null).
      There is a lot to digest in there, but you probably need to spend more time with the SDK documentation.
    • vichug
      Jul 09 2013 | 8:03 pm
      since i am currenty going through this, here's a concise external tutorial, albeit dating back to max 4.6 unfortunately : http://www.music.mcgill.ca/~ich/classes/mumt402_06/MaxMSPExternalsTutorials/MaxMSPExternalsTutorial3.2.pdf
      and these "Flop" xcode projects by Nicolas Danet are a precious set of dummies for beginners like us : https://github.com/nicolasdanet/Flop and i could advise to begin with doing some tutorials, it might seem long and too much for a beginning, but it is really a timesaver to know some basics about what you are doing.
    • José López-Montes
      Jul 09 2013 | 10:57 pm
      Thank you very much to all posters for the astonishing quick responses. Luigi, your code is right. As you all say, I must spent a lot of time exploring the SDK. I'm just at the beginning with development. See you on the net! jlm