c and c++
Author
Hi guys,
I have a program that uses a c and a c++ compiler and then links the results into one app. I know this isnt pretty but there is no way to prevent it in this app.
Now my problem is that I want to pass a class from the c++ side to the c side. Since c doesnt have classes I am looking for a workaround.
Is it maybe possible to have the c++ class inherit from a struct which declares the functions required and then pass a pointer to that struct?
Any other ideas that are have way pretty?
-CProgrammer
Hoboy.
On one end of the spectrum, you have a C interface which might look like this:
This is relatively easy -- you can define the structure on the C++ side of things only, and in C++, structures and classes are synonymous (with only effects on default access). The functions you can define inline to your C++ with `extern "C"`. The C API only interacts with myclass*, never myclass, so it doesn't even need to know the definition. This lets you use a non-POD myclass.
On the other hand, you may have a class which you need to store on the stack in your C code, involving virtual functions. In this case, you basically have to implement the class in C:
And no, you can't clean up the syntax for your C++ code without doing one of the following:
1) Invoking undefined behavior
2) Wrapping the entire thing
[Edited by - MaulingMonkey on May 23, 2007 10:28:39 AM]
On one end of the spectrum, you have a C interface which might look like this:
struct myclass;typedef struct myclass myclassptr;myclassptr CreateMyClass( ... );void DestroyMyClass( myclassptr );unsigned GetMyClassMember( myclassptr );This is relatively easy -- you can define the structure on the C++ side of things only, and in C++, structures and classes are synonymous (with only effects on default access). The functions you can define inline to your C++ with `extern "C"`. The C API only interacts with myclass*, never myclass, so it doesn't even need to know the definition. This lets you use a non-POD myclass.
On the other hand, you may have a class which you need to store on the stack in your C code, involving virtual functions. In this case, you basically have to implement the class in C:
typedef struct myclass_vtable { unsigned (*get_member)( myclassptr );} *myclass_vtable_ptr;struct myclass { /* special */ myclass_vtable_ptr _vtable; /* public */ ... /* private */ unsigned _a, _b;};unsigned GetMyClassMemberDefaultImpl( myclassptr self ) { return self->_a + self->_b;}myclass_vtable default_vtable = { &GetMyClassMemberDefaultImpl};void InitializeMyClass( myclassptr self ) { self->_vtable = &default_vtable; self->_a = 42; self->_b = 24;}void CleanupMyClass( myclassptr self ) { /* any cleanup code that might be necessary */}unsigned GetMyClassMember( myclassptr self ) { return (*(self->_vtable->get_member))( self );}And no, you can't clean up the syntax for your C++ code without doing one of the following:
1) Invoking undefined behavior
2) Wrapping the entire thing
[Edited by - MaulingMonkey on May 23, 2007 10:28:39 AM]
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
