how do you write a c wrapper for a c++ class with inheritance

Question

I was just wondering if there was a way to create a c wrapper API for a c++ class that has inheritance.

Consider the following:

class sampleClass1 : public sampleClass{

  public:
    int get() { return this.data *2; };
    void set(int data);
}


class sampleClass : public sample{

  public:
   int get() { return this.data; }
   void set(int data) {this.data = data; }
}

class sample {

 public:
   virtual int get();
   virtual void set(int data);

 private:
   int data;

}

How would I wrap the sampleClass1 to make it work in a c context ???

thanks,

Answer 1

First, your sample should really get a proper virtual dtor.

Next, just add one free function with C-binding for each function which is part of the interface, simply delegating:

"sample.h"

#ifdef __cplusplus
extern "C" {
#endif
typedef struct sample sample;
sample* sample_create();
sample* sample_create0();
sample* sample_create1();
void sample_destroy(sample*);
int sample_get(sample*);
void sample_set(sample*, int);
#ifdef __cplusplus
}
#endif

"sample-c.cpp"

#include "sample.h" // Included first to find errors
#include "sample.hpp" // complete the types and get the public interface

sample* sample_create() {return new sample;}
sample* sample_create0() {return new sampleClass;}
sample* sample_create1() {return new sampleClass1;}
void sample_destroy(sample* p) {delete p;}
int sample_get(sample* p) {return p->get();}
void sample_set(sample* p, int x) {p->set(x);

"sample.hpp"

// Your C++ header here, with class definition

"sample.cpp"

#include "sample.hpp" // Included first to find errors
// Implement the class here