Example of how to access a static C++ class instance from C.

README.txt

Example of how to access a static C++ class instance from C.

main.c

// Compile this as a C file:

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

void show(int data[], int n) {
    for (int i=0; i<n; i++) {
        printf("%d ", data[i]);
    }
    printf("\n");
}

int main(void) {

  // Set class attribute instance via wrapper:
  int data[] = {1, 2, 3};
  init(data);
  
  // Access class attribute via pointer:
  show(mydata, 3);
  mydata[0] = 10;
  show(mydata, 3);
}

Makefile

%.o: %.c
	gcc -c $<

%.o: %.cpp
	g++ -c $<

main: main.o mylib.o
	gcc $^ -o $@

clean:
	rm -f main *.o

mylib.cpp

// Compile this as a C++ file:

#include "mylib.h"

// Since this is compiled as C++, mydata can be assigned the address of
// the static class instance's data attribute:
static MyClass myclass;
extern int *mydata = myclass.data;

// C functions:
extern "C" {
  void init(int data[3]) {
    myclass.set(data);
  }
}

mylib.h

#include <stdint.h>
#include <stdlib.h>

// C++ definitions:
#ifdef __cplusplus

class MyClass {
 public:
  int data[3];
  MyClass() { set(0); }
  void set(int data[]) {
    for (int i=0; i<3; i++) {
      this->data[i] = data[i];
    }
  }
  void set(int d) {
    for (int i=0; i<3; i++) {
      this->data[i] = d;
    }
  }    
};

#endif

// C access points that use C++ code:
#ifdef __cplusplus
extern "C" {
#endif

  // mydata is set in mylib.cpp:
  extern int *mydata;
  void init(int data[3]);

#ifdef __cplusplus
}
#endif