Exposing Interfaces

Hourglass Interfaces for C++ Api

HourGlass Interfaces

Using C/C++ for performance is the usual thing. But to get other languages to take advantage of this requires a bit of setup.

Start with any C++ object.

\\\ cpp_object.h
\\\ Can be any cpp object

class CppObject{
  void doSomething(){}
}



The extern “C” is wrapper important because the C compiler will have linkage errors. Forward declares cpp_object_interface

\\\ hourglass_interface.h


#ifdef __cplusplus /// This is important, otherwise it will have linkage errors
extern "C" {
#endif

  typedef struct cpp_object_interface* cpp_object_pointer;
  
  cpp_object_pointer constructor();
  void destructor(cpp_object_pointer cpp_object);

  void cpp_object_doSomething(cpp_object_pointer cpp_object);

#ifdef __cplusplus /// This is important, otherwise it will have linkage errors
}
#endif



Implements the struct cpp_object_interface to include the original cpp object.
Constructor uses malloc(), then casted to object. Destructor uses the free() method.

\\\ hourglass_interface.cpp

#include "cpp_object.h"

extern "C" { /// This is important, otherwise it will have linkage errors

  struct cpp_object_interface{
    CppObject originalCppObject;
  }

  cpp_object_pointer constructor(){
    return (cpp_object_pointer) malloc(sizeof(cpp_object_pointer));
  }

  void destructor(cpp_object_pointer cpp_object){
    free(cpp_object);
  }

  void cpp_object_doSomething(cpp_object_pointer cpp_object){
    cpp_object->originalCppObject.doSomething();
  }

}



Ready for binding

Bindings for other languages are now possible. There are some edge cases like using specific types like int32_t in the C interfaces but that will be a whole topic by itself.