Question

i’d like to write a wrapper for a C++ framework. this framework is kinda buggy and not really nice and in C++. so i’d like to be able to call their methods from outside (via good old C file) of their framework by using just one shared lib. this sounds like the need for a wrapper that encapsulates the wanted framework methods for usage with C instead of C++.

So far so good…. here is what i already did:

interface aldebaran.h
(this is in my include folder, the ultrasound methods should be called from outside of the framework):

#ifndef _ALDEBARAN_H
#define _ALDEBARAN_H

#ifdef __cplusplus
 extern "C" {
#endif

void subscribe_ultrasound();
void unsubscribe_ultrasound();
float read_ultrasound();

#ifdef __cplusplus
}
#endif

#endif

now the wrapper:

cpp file aldebaran.cpp:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "aldebaran.h"
#include "alproxy.h"
#include "../../include/aldebaran.h"

/*
 * Ultrasound defines
 */
#define ULTRASOUND_RESERVATION_MAGIC  "magic_foobar"

#define ULTRASOUND_POLL_TIME          250
#define ULTRASOUND_READ_ATTEMPTS      50
#define ULTRASOUND_SLEEP_TIME         20

using namespace std;
using namespace AL;

/*
 * Framework proxies
 */
ALPtr<ALProxy> al_tts;
ALPtr<ALProxy> al_led;
ALPtr<ALProxy> al_motion;
ALPtr<ALProxy> al_mem;
ALPtr<ALProxy> al_us;
ALPtr<ALProxy> al_cam;
ALPtr<ALProxy> al_dcm;

/*
 * Constructor
 */
Aldebaran::Aldebaran(ALPtr<ALBroker> pBroker, std::string pName): ALModule(pBroker, pName)
{
    try {
        al_tts    = this->getParentBroker()->getProxy("ALTextToSpeech");
        al_led    = this->getParentBroker()->getProxy("ALLeds");
        al_motion = this->getParentBroker()->getProxy("ALMotion");

        al_mem    = this->getParentBroker()->getProxy("ALMemory");
        al_us     = this->getParentBroker()->getProxy("ALUltraSound");
        al_cam    = this->getParentBroker()->getProxy("NaoCam");
        al_dcm    = this->getParentBroker()->getProxy("DCM");
    }catch(ALError& err){
        std::cout << "XXX: ERROR: " << err.toString() << std::endl;
        return 1;
    }

    printf("XXX: module aldebaran initiated\n");
    fflush(0);
}

/*
 * Destructor
 */
Aldebaran::~Aldebaran()
{
    printf("XXX: module aldebaran destructed\n");
    fflush(0);
}

/*
 * Subscribe to ultrasound module
 */
void subscribe_ultrasound()
{
    ALValue param;

    param.arrayPush(ULTRASOUND_POLL_TIME);
    al_us->callVoid("subscribe", string(ULTRASOUND_RESERVATION_MAGIC), param);

    printf("XXX: ultrasound subscribed: %s\n", ULTRASOUND_RESERVATION_MAGIC);
    fflush(0);
}

/*
 * Unsubscribe to ultrasound module
 */
void unsubscribe_ultrasound()
{
    al_us->callVoid("unsubscribe", string(ULTRASOUND_RESERVATION_MAGIC));

    printf("XXX: ultrasound unsubscribed: %s\n", ULTRASOUND_RESERVATION_MAGIC);
    fflush(0);
}

/*
 * Read from ultrasound module
 */
float read_ultrasound()
{
    int i;
    float val1, val2;
    float val_sum;
    ALValue distance;

    val_sum = .0f;

    for(i = 0; i < ULTRASOUND_READ_ATTEMPTS; ++i){
        SleepMs(ULTRASOUND_SLEEP_TIME);

        distance = al_mem->call<ALValue>("getData", string("extractors/alultrasound/distances"));
        sscanf(distance.toString(AL::VerbosityMini).c_str(),"[%f, %f, \"object\"]", &val1, &val2);

        val_sum += val1;
    }

    return val_sum / (1.f * ULTRASOUND_READ_ATTEMPTS);
}

definition file for aldebaran.cpp:

#ifndef ALDEBARAN_API_H
#define ALDEBARAN_API_H

#include <string>

#include "al_starter.h"
#include "alptr.h"

using namespace AL;

class Aldebaran : public AL::ALModule
{
    public:
        Aldebaran(ALPtr<ALBroker> pBroker, std::string pName);

        virtual ~Aldebaran();

        std::string version(){ return ALTOOLS_VERSION( ALDEBARAN ); };

        bool innerTest(){ return true; };
};

#endif

So this should be a simple example for my wrapper and it compiles fine to libaldebaran.so.

now my test program in C:

… now i’d like to call the interface aldebaran.h methods from a simple c file like this:

#include <stdio.h>

/*
 * Begin your includes here...
 */

#include "../include/aldebaran.h"

/*
 * End your includes here...
 */

#define TEST_OKAY    1
#define TEST_FAILED  0

#define TEST_NAME "test_libaldebaran"

unsigned int count_all = 0;
unsigned int count_ok  = 0;

const char *__test_print(int x)
{
    count_all++;

    if(x == 1){
        count_ok++;

        return "ok";
    }

    return "failed"; 
}

/*
 * Begin tests here...
 */

int test_subscribe_ultrasound()
{
    subscribe_ultrasound();

    return TEST_OKAY;
}

int test_unsubscribe_ultrasound()
{
    unsubscribe_ultrasound();

    return TEST_OKAY;
}

int test_read_ultrasound()
{
    float i;

    i = read_ultrasound();

    return (i > .0f ? TEST_OKAY : TEST_FAILED);
}

/*
 * Execute tests here...
 */

int main(int argc, char **argv)
{
    printf("running test: %s\n\n", TEST_NAME);

    printf("test_subscribe_ultrasound:    \t %s\n", __test_print(test_subscribe_ultrasound()));
    printf("test_read_ultrasound:         \t %s\n", __test_print(test_read_ultrasound()));
    printf("test_unsubscribe_ultrasound:  \t %s\n", __test_print(test_unsubscribe_ultrasound()));

    printf("test finished: %s has %u / %u tests passed\n\n", TEST_NAME, count_ok, count_all);

    return (count_all - count_ok);
}

how can i manage to call these methods? i mean within my C file i have no possibility to create such an object-instance (that generated all the needed ALProxies), have i?

help would be really appreciated… thx

---

thank you very much so far!!

as xtofl said.. i’d like to keep my interface as simple as possible (without another c++ object preferably):

#ifndef _ALDEBARAN_H
#define _ALDEBARAN_H

#ifdef __cplusplus
 extern "C" {
#endif

void subscribe_ultrasound();
void unsubscribe_ultrasound();
float read_ultrasound();

#ifdef __cplusplus
}
#endif

#endif

the problem hereby is that functions like subscribe_ultrasound() cannot be called without the instanciation of all the proxies… this is our precondition:

...
        al_tts    = this->getParentBroker()->getProxy("ALTextToSpeech");
        al_led    = this->getParentBroker()->getProxy("ALLeds");
        al_motion = this->getParentBroker()->getProxy("ALMotion");

        al_mem    = this->getParentBroker()->getProxy("ALMemory");
        al_us     = this->getParentBroker()->getProxy("ALUltraSound");
        al_cam    = this->getParentBroker()->getProxy("NaoCam");
        al_dcm    = this->getParentBroker()->getProxy("DCM");
...

if i don’t have the code above called, all other will fail.

within their framework it is possible to “autoload” my libaldebaran.so via a python script like this call:

myModule = ALProxy("Aldebaran",  global_params.strRemoteIP, global_params.nRemotePort );

The framework log then says:

May 10 15:02:44 Hunter user.notice root: XXX: module aldebaran initiated
May 10 15:02:46 Hunter user.notice root: INFO: Registering module : 'Aldebaran'
May 10 15:02:46 Hunter user.notice root: ______ End of loading libraries ______

which is totally okay… it called the constructor of my module (so all other needed proxies got instanciated too).

but of course this instance does not belong to my C program…

maybe there is a possibility to share this to all other processes?

Answer 1

You said yourself to create a C wrapper API around an OO framework.

This means you don’t need any objects passing the wrapper API (as it appears from the decribed header). It seems all objects needed are created/destructed behind the wrapper API, out of view of your test program.

The first seems the case. You don’t need objects to test your wrapper API. In the end, all objects are bytes (in memory) that are accessed through a fixed set of functions. It doesn’t matter much whether the functions are written as member-functions (C++) or as plain C functions, as long as they obey the intended semantics of your objects.