animal.cpp

#include "animal.h"

void Animal::inc(int i){
  this->counter += i;
}

void Animal::say(){
  std::cout << this->counter << std::endl;
}

animal.h

#include <iostream>

class Animal
{
public:
  int counter;

  void inc(int);
  void say();
};

error

main.nim(14)             main
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

main.min

{.compile: "/Users/sherjilozair/NimProjects/nim-sfml/animal.cpp".}

const header = "/Users/sherjilozair/NimProjects/nim-sfml/animal.h"

type
  AnimalObj {.header: header, importcpp: "Animal".} = object
  Animal = ptr AnimalObj

proc say(animal: Animal) {.importcpp: "#.say(@)".}
proc inc(animal: Animal, i: cint) {.importcpp: "#.inc(@)".}

when isMainModule:
  var x: Animal
  x.say()
  x.inc(10)
  x.say()