Accessing c++ class member functions from c file

Question

I am implementing a c++ class based library file. I need to link this library to both c file and c++ file. I guess, there will be no issues instantiating the class from c++ file. I do find a way to instantiate the class from c file aswell, but it seems I need to pass the object every time while a function call. Is there any way i could use the instantiated object directly in c file to call a member function?

Find the code sample below,

Myclass.h

#ifndef __MYCLASS_H
#define __MYCLASS_H

class MyClass {
        private:
                int m_i;
        public:
                void int_set(int i);

                int int_get();
};

#endif

MyClass.cc

#include "MyClass.h"
void MyClass::int_set(int i) {
        m_i = i;
}

int MyClass::int_get() {
        return m_i;
}

MyMain_c++.cc

#include "MyClass.h"
#include <iostream>

using namespace std;

int main(int argc, char* argv[]) {
        MyClass *c = new MyClass();
        c->int_set(3);
        cout << c->int_get() << endl;
        delete c;
}

MyWrapper.h

#ifndef __MYWRAPPER_H
#define __MYWRAPPER_H

#ifdef __cplusplus
extern "C" {
#endif

typedef struct MyClass MyClass;

MyClass* newMyClass();

void MyClass_int_set(MyClass* v, int i);

int MyClass_int_get(MyClass* v);

void deleteMyClass(MyClass* v);

#ifdef __cplusplus
}
#endif
#endif

MyWrapper.cc

#include "MyClass.h"
#include "MyWrapper.h"

extern "C" {
        MyClass* newMyClass() {
                return new MyClass();
        }

        void MyClass_int_set(MyClass* v, int i) {
                v->int_set(i);
        }

        int MyClass_int_get(MyClass* v) {
                return v->int_get();
        }

        void deleteMyClass(MyClass* v) {
                delete v;
        }
}

MyMain_c.c

#include "MyWrapper.h"
#include <stdio.h>

int main(int argc, char* argv[]) {
        struct MyClass* c = newMyClass();
        MyClass_int_set(c, 3); // issue : i need to send the object 
                                          everytime
        // c->int_set(3); any ways of using like this??
        printf("%i\n", MyClass_int_get(c));
        deleteMyClass(c);
}

Unrelated to your problem, but please read [What are the rules about using an underscore in a C++ identifier?](https://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier) — Some programmer dude, Mar 26 '18 at 14:40
As for your problem, no there's really no other way to do it. C is not C++. If you want to use C++ object you need some way to actually pass the object to the functions that needs it. That kind of how C++ works internally as well, when calling a member function the object is passed as a kind of hidden first argument. — Some programmer dude, Mar 26 '18 at 14:45
What do you mean? No matter what you do, you always need the instance and the function. In C++, it is `obj->foo()`, in `C` is it `foo(obj)`. It is really unclear what is your goal. There is no analogue to Pascal's `with` keyword in C or C++, if this is what you are asking about. — SergeyA, Mar 26 '18 at 14:45

score -1 · Answer 1 · answered Mar 26 '18 at 15:15

#include "MyClass.h"
#include "MyWrapper.h"

extern "C" {
    MyClass* newMyClass() {
            return new MyClass();
    }

    void MyClass_int_set(MyClass* v, int i) {
            v->int_set(i);
    }

    int MyClass_int_get(MyClass* v) {
            return v->int_get();
    }

    void deleteMyClass(MyClass* v) {
            delete v;
    }
}

Accessing c++ class member functions from c file

1 Answers1