Re: lug-bg: c/c++ differences

[Nikolay Mitev]

Hi,

> i wse pak reshenie imalo za koeto ne se bqh setil
> extern "C"
> samo deto trqbwa da poexperimentiram s towa
> zashtoto ne sym siguren kakwo shte se poluchi
> s polimorfizma :)
> 10x za otgowora wse pak :)
> 

kakuv polimorphism te goni be 4ovek? Nqma takuv film tuka. Ima6 ptr kum
funkciq. Nqma6 obekt, nqma6 ni6to.  Kakuv polymorphism bez obekt?  Eti te
elegantno re6enie na problema ti s polymorphism.

main program:

obtest.h
======

class Test {
 public:
  virtual void do_something () const {
    std::cout << "Shit, no polymorphism :-(" << std::endl;
  }
};

======

main.cpp

======
#include <iostream>
#include <dlfcn.h>

#include "obtest.h"

int main () {

  void *d = dlopen ("libtest.so", RTLD_NOW);

  if (d == 0) {
    std::cout << "Can't find library" << std::endl;
  }

  Test* (*object_factory) () = (Test* (*) ()) dlsym (d, "object_factory");
  Test* t;
  if (object_factory != 0) {
    t = object_factory ();
  } else {
    std::cout << "Can't find function" << std::endl;
    exit (1);
  }
  
  t->do_something ();
}

======

plugin:

test.cpp

======

#include <iostream>

#include "obtest.h"

class Test1 : public Test {

public:

  virtual void do_something () const {
    std::cout << "Wow, polymorphism" << std::endl;
  }
};

static Test1 test;

extern "C" {
  Test* object_factory () {
    return &test;
  }
}

======

test.cpp kompilira6 s g++ -shared -olibtest.so test.cpp

drugoto g++ -otest main.cpp i runva6.

Kratko obqsnenie.:
Izpolzva6 plugin-a kato faktory za obekti. Func-a ti vru6ta ptr KUM OBEKT.
Prez nego kato vikne6 funkciq ima6 ve4e polymorphism v deijstvie.

N.B. Naro4no test v plugina e static, za6toto ne e hubavo da se zadelq pamet
v dll i da se osvobozhdava v main, naprimer, za6toto mozhe dll-a i app-a da
izpolzvat razli4ni heap-ove i da stane boza. Zatova ako zadelq6 v factory-to
dinami4no, napravi i o6te edna func destroy (void *), naprimer, v plugin-a, s
koqto da osvobozhdava6 zadelenata pamet pak v konteksta na plugin-a.

E, dano sum pomognal.

cheers,
face




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