Wrapping C++ void functions with pybind11

Question

I have a C++ class containing void functions which take STL vectors passed by reference and modify the contents of one of those vectors. For example:

void somefunction(std::vector<double> &result, std::vector<double> &array1, std::vector<double> &array2) {some calculations}

And the pybind11 binding looks like this:

.def("somefunction", &somefunction)

I have included the 'pybind11/stl.h' header file which handles the automatic conversion between STL containers and python equivalents and in Python I call somefunction with Python lists but I'm not sure if the C++ layer can modify the result Python list.

My then question is how to write Python bindings for C++ functions which modify the contents of an STL vector passed by reference and return void.

Sergei · Accepted Answer · 2018-04-23 08:14:54Z

2

Including pybind11/stl.h results to copy-conversions between c++ and pyhton, see http://pybind11.readthedocs.io/en/stable/advanced/cast/stl.html#automatic-conversion

To pass by reference see section http://pybind11.readthedocs.io/en/stable/advanced/cast/stl.html#making-opaque-types

answered Apr 23, 2018 at 8:14

Sergei

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2 Comments

fbartolic Over a year ago

So if I understood the docs correctly, I should make use of the PYBIND11_MAKE_OPAQUE() macro and a corresponding class_ declaration? What do I then pass to somefunction in Python?

Sergei Over a year ago

You should pass a python counterpart of your std::vector<int>, the VectorOfInt. Something like a = VectorOfInt([1,2]); b = VectorOfInt([1,2]); somefunction(a, b) I believe.

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