C++ user module

[ma261065]

I've been using someone else's code as a c++ user module for a while, following the example at examples/usercmodule/cppexample

However, the maintainer of the original code has recently started using c++ vector

Since the user module declaration has to be compatible with C everything goes in extern "C" scope, and declarations like vector<uint32_t> mylist don't work.

Am I correct in understanding that a "C++ User module" can use C++ syntax in the source file, but we are limited to "C compatible" in function declarations etc?

[bikeNomad]

You are correct (if I understand you correctly). C++ code can use C++ functions/methods internally; it's just that the functions that are called by Python code must be callable from C (no name mangling, etc.). You can ensure this by declaring them as extern "C" (with #ifdef __cplusplus guards). You also need to be careful with memory allocation, C++ exceptions and static guards, etc.

You could use a std::vector inside your C++ code, but if you wanted to provide it to MicroPython code it'd have to be presented as a bytes or array.array object or similar. You could use std::vector::cbegin() to get a pointer to the start of the allocated memory.

[cnadler86]

I have some similar topics. Does anyone have an example?
I want to use a cpp Objekt in my User Module anf don't know how to integrate it...

[cnadler86]

I found some example code of a binding for c++ here.

Didn't test, if it works, but I could at least build a module with that structure.

Basically the module registration happens in c, while the User Module is in c++ (locals). For this, the stand Makros MP_DEFINE_CONST_FUN_OBJ_xxx were extended in order to be c++ compatible.

Is this a good practice?