对 Py_Initialize() 的未定义引用

Question

I was trying to embed some Python into a C program, but first I was testing some elementary operations as seen in the following code:

#include <stdio.h>
#include <stdlib.h>
#include <random>
#include <chrono>
#include <iostream>
#include <math.h>
#include <Python.h>

int main()
{
    Py_Initialize();
    PyRun_SimpleString("print('Hello world')");
    Py_Finalize();

    // Some C code
}

It turns out that (a) the makefile does build well the program when commenting out the Python-related lines (Py_Initialize, PyRun_SingleString, Py_Finalize), (b) however, when adding the Python lines, the build returns the following error:

g++ -o program program.cpp -lm -std=c++11 -O3 -I/usr/include/python3.6m/
/tmp/ccgiujXn.o: In function `main':
program.cpp:(.text.startup+0x62): undefined reference to `Py_Initialize'
program.cpp:(.text.startup+0x70): undefined reference to `PyRun_SimpleStringFlags'
program.cpp:(.text.startup+0x75): undefined reference to `Py_Finalize'
collect2: error: ld returned 1 exit status
Makefile:2: recipe for target 'exec_program' failed
make: *** [exec_program] Error 1

Do you know why this error occurs? I thought that the Python.h header was correctly added, but it does not seem to be the case when adding the Python lines. My makefile is:

exec_program:  program.cpp
    g++ -o program program.cpp -lm -std=c++11 -O3 -I/usr/include/python3.6m/
    ./program
    rm program

I am using Ubuntu 18.04.4 LTS, g++ 7.4.0, Python 3.6.9 (/usr/lib/) and 3.7.6 (/home/anaconda3/lib).

Sorry if you find the question is reiterative, but I thought no other post had a solution for my problem.

Thanks in advance for any help!

Answer 1

您必须使用-l链接库

Answer 2

You should not compile your module as stand alone executable, but rather as shared library object *.so , so objects line Py_Initialize will be avaliable at run time. The suggested by documentation way is

from distutils.core import setup, Extension

module1 = Extension('demo',
                   define_macros = [('MAJOR_VERSION', '1'),
                                 ('MINOR_VERSION', '0')],
                   include_dirs = ['/usr/local/include'],
                   libraries = ['tcl83'],
                   library_dirs = ['/usr/local/lib'],
                   sources = ['demo.c'])

setup (name = 'PackageName',
      version = '1.0',
      description = 'This is a demo package',
      author = 'Martin v. Loewis',
      author_email = 'martin@v.loewis.de',
      url = 'https://docs.python.org/extending/building',
      long_description = '''
This is really just a demo package.
''',
      ext_modules = [module1])

The distutils module will generate correct gcc command for you.

You can read more about building python modules at official documentation https://docs.python.org/3/extending/building.html#building

Answer 3

添加/usr/lib/x86_64-linux-gnu/库目录和python3.6m库：

g++ -o program program.cpp -lm -std=c++11 -O3 -I/usr/include/python3.6m/ -L /usr/lib/x86_64-linux-gnu/ -lpython3.6m