CODEWITHSUNDEEP
c++callbacknamespaces
user1190832
user1190832

Reputation:

Callbacks from C code using C++ code?

I am using a driver written in pure C. It has some callbacks registered to it. When those are called they will interact with C++ code.

I tried to access functions in a namespace in the callback but that have me an error which made me think they can't call C++ code which makes a lot of sense I guess. But then I realized I was interacting with C++ classes with no problem.

So is it allowed for a callback executed in C code to call C++ specific functioanlity like namespaces and classes?

Upvotes: 0

Views: 102

Answers (2)

utnapistim
utnapistim

Reputation: 27365

So is it allowed for a callback executed in C code to call C++ specific functioanlity like namespaces and classes?

Yes. The usual solution to this is to create an opaque (void*) object that holds the pointer of your class, and a set of callbacks declared as extern "C" in your C++ code, that receive the void *, reinterpret_cast it to your class pointer and call the appropriate functions.

If you do not need classes remembered for your callbacks, you can dispense of the void* and the reinterpret_cast stuff but the callbacks in C++ still need to be declared as extern "C" for the C code to be able to call them.

Upvotes: 0

Paul Evans
Paul Evans

Reputation: 27567

You need to #include the header as a C file:

extern "C" {
    #include "c_file.h"
}

Upvotes: 2

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