C wrapper for C++

[anand102]

hi,

i want to write C wrappers around exisitng C++ code. any suggestions
on how to do that. in what situations wrappers can be used and in what
situations we should avoid writing the wrappers ?

thnaks

 

[Zyrenthian]

I believe i have seen it as
#ifdef C_PLUS_PLUS
class myClass
#endif

Not 100% tho It was something along these lines

Matt

 

[anand102]

thanks,

but i am talking for 100% pure C code where i cant use classes.
what about writng extern "C" functions ?? what is there limitations ??

 

[Cagliostro]

use that
//a supposing xx.h
#if defined(CPP)
class xxx
{
public:
xxx* functionX();
};
#endif
#if defined(CPP)
#extern "C"
{
#endif
//a C shared funcrtion here
#if defined(CPP)

void* c_functionX(void*);

#extern "C"
{
#endif

//a supposed xx.lib is generated in C++ from this code
//from this cpp file
//xx.cpp
void* c_functionX(void* c)//handle to a xxx class
{
return (void*)((xxx*)c)->functionX();
}
John Fill

ivfmd@mail.md

 

[Cagliostro]

Some little changes in the code above:
the h file:

#if defined(C_PLUS_PLUS)
//this is define for borland.
//may exists other defines for VisualC++...
//code visible only from C++
class xxx
{
public:
xxx* functionX();
};
#endif
#if defined(C_PLUS_PLUS)
extern "C"{
#endif

//a C shared funcrtion here
//code visible from both, C and C++. This one you can
//implement in C++ without problems.
void* c_functionX(void*);

#if defined(C_PLUS_PLUS)
extern "C"}
#endif

the cpp file there


//a supposed xx.lib is generated in C++ from this code
//from this cpp file
//xx.cpp
void* c_functionX(void* c)//handle to a xxx class
{
return (void*)((xxx*)c)->functionX();
}
John Fill

ivfmd@mail.md

 

[anand102]

that's fine.
but i want the header to be visible from C compiler also.
for that i was thinking about something like

#if defined(C_PLUS_PLUS)
class xxx
{
public:
xxx* functionX();
};

#else

struct xxx xxx;

#endif

does it make sense to you ??

 

[ankan]

How about this...

/* ... */
struct xxx {
#if defined(C_PLUS_PLUS)
private:
#endif
/* the private variables to be declared
* ...
*/
#if defined(C_PLUS_PLUS)
/* the private functions (if any)
* ...
*/
protected:
/* the protected functions (if any)
* ...
*/
#endif
/* the protected variables (if any)
*
*/
#if defined(C_PLUS_PLUS)
public:
/* the public functions (if any)
*
*/
#endif
/* the public variables (if any)
* ...
*/
};
/* ... */

In this way, if its C then you will get a structure with all the variables available (publicly!), and if it is C++ it will be a just like the class required. Although, if you make all the variables available in C (you have to, in case you want to use them), then a basic concept of OOP, data hiding is violated (I guess). But then you got to do what you got to do!!;-)
But you don't get the functions in this way.:-( Ankan.

Please do correct me if I am wrong. s-)

 

[Cagliostro]

The function you will see on both, C and C++. Implementation you will port on a LIB and will compille in C++. So you will compille C projects with this .lib(implementation) and this .h(declarations). If you see, many windows (not all of them)functions are implemented in C++ but accesible from C. They receive a handle, what usually is nothing more than a pointer to a C++ class. So when you compille C project you use .lib what you don't know if they are implemented in C or C++. John Fill

ivfmd@mail.md