使用 cython 和 cythonize 从 python 调用 C++ function

Question

I'm trying to learn Cython, and I want to call a simple C++ function from python

When building, I either have a uio.obj: error LNK2001: unresolved external symbol _just_a_func , or when I tried different combinations of cython prototypes, my just_a_func() function does not land in my module.

Here is all the code, setup.py, test.py, .pxd, .pyx and.h

########################
### uio.h
########################
#include <string>
using namespace std;
struct uio{
    int i;
    uio():i(2){}
    float f;
    string s;
    // float fun(int a);
    float fun(int a){return float(a+i);}

};

// int just_a_func(string s);
int just_a_func(string s){return s.length();}


########################
### uio.pxd
########################
from libcpp.string cimport string

cdef extern from "uio.h":
    cdef extern int just_a_func(string s)


########################
### uio.pyx
########################
# distutils: language = c++

from uio cimport just_a_func
cdef extern int just_a_func(s):
    return just_a_func(s)


########################
### setup.py
########################
# python .\setup.py build_ext --inplace --compiler=msvc

from setuptools import setup

from Cython.Build import cythonize

setup(ext_modules=cythonize("uio.pyx"))

########################
### test2.py
########################
import uio
print(dir(uio))
print("just_a_func", uio.just_a_func("fdsfds"))

Answer 1

May be, the explicit definition your function as "clear C" is helping you. In any case, your error message specifies that type of function. Try this:

extern "C" {
  int just_a_func(string s){return s.length();}
}

Answer 2

Found a solution on https://dmtn-013.lsst.io/

This is the working solution

########################
### uio.h
########################
#include <string>
using namespace std;

int just_a_func(string s){return s.length();}


########################
### uio.pxd
########################
from libcpp.string cimport string
cdef extern from "uio.h":
    int just_a_func(string s)


########################
### uio.pyx
########################
# distutils: language = c++
# note the "as", this is a trick to avoid name clash, to allow the same function name
from uio cimport just_a_func as cjust_a_func

def just_a_func(s):
    return cjust_a_func(s)


########################
### setup.py
########################
# python .\setup.py build_ext --inplace --compiler=msvc

from setuptools import setup

from Cython.Build import cythonize

setup(ext_modules=cythonize("uio.pyx"))

########################
### test2.py
########################
import uio
from sys import argv
print(dir(uio))
print("just_a_func", uio.just_a_func((argv[1].encode())))