Embedding Python in C, linking fails with undefined reference to `Py_Initialize'

问题

I am trying to compile the example from the docs https://docs.python.org/2.7/extending/embedding.html and my code looks exactly like the one under 5.1:

#include <Python.h>

int
main(int argc, char *argv[])
{
  Py_SetProgramName(argv[0]);
  Py_Initialize();
  PyRun_SimpleString("from time import time, ctime\n"
                     "print 'Today is', ctime(time())\n");

  Py_Finalize();
  return 0;
}

I use the following command to compile it which works fine for me and gives me the desired object file:

gcc -c $(python2.7-config --cflags) embedpy.c

To link it I use the following command which ends up in the following error:

gcc $(/usr/bin/python2.7-config --ldflags) embedpy.o
embedpy.o: In function `main':
/home/miguellissimo/embedpy.c:6: undefined reference to `Py_SetProgramName'
/home/miguellissimo/embedpy.c:7: undefined reference to `Py_Initialize'
/home/miguellissimo/embedpy.c:8: undefined reference to `PyRun_SimpleStringFlags'
/home/miguellissimo/embedpy.c:11: undefined reference to `Py_Finalize'
collect2: error: ld returned 1 exit status

I can't find out what I am doing wrong or what I forget to get the example working.

PS: The python2.7-config command gives the following output on my Xubuntu machine:

>>> python2.7-config --cflags 
-I/usr/include/python2.7 -I/usr/include/x86_64-linux-gnu/python2.7  -fno-stri
ct-aliasing -D_FORTIFY_SOURCE=2 -g -fstack-protector --param=ssp-buffer-size=
4 -Wformat -Werror=format-security  -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-pr
ototypes

>>> python2.7-config --ldflags
-L/usr/lib/python2.7/config-x86_64-linux-gnu -L/usr/lib -lpthread -ldl  -luti
l -lm  -lpython2.7 -Xlinker -export-dynamic -Wl,-O1 -Wl,-Bsymbolic-functions

回答1:

Libraries have to come after the object files when you are linking, so do:

gcc  embedpy.o $(/usr/bin/python2.7-config --ldflags)

回答2:

I replicated the same problem on Lubuntu14.04 32bit virtual machine running on Win7 machine.

I did the following things to replicate the problem in the first place where the C++ code is written in Eclipse C/C++ IDE. Defined a C++ Eclipse project titled "test". The source file contains the following C++ code which is the same as mentioned above by Miguellissimo.

C++ Code ::

#include "python2.7/Python.h"

int main(int argc, char *argv[]) {

    Py_Initialize();
    PyRun_SimpleString("print \"Hello, world!\"");

    Py_Finalize();
    return 0;
}

Errors ::

test.o: In function main': /home/ros/workspace/test/src/test.cpp:15: undefined reference toPy_Initialize' /home/ros/workspace/test/src/test.cpp:17: undefined reference to PyRun_SimpleStringFlags' /home/ros/workspace/test/src/test.cpp:18: undefined reference toPy_Finalize' collect2: error: ld returned 1 exit status

The output of the following commands was the same as mentioned before by Miguellissimo,

ros@rosPC:~/workspace/test/src$ python2.7-config --cflags

-I/usr/include/python2.7 -I/usr/include/i386-linux-gnu/python2.7  -fno-strict-aliasing -D_FORTIFY_SOURCE=2 -g -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security  -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes

ros@rosPC:~/workspace/test/src$ python2.7-config --ldflags

-L/usr/lib/python2.7/config-i386-linux-gnu -L/usr/lib -lpthread -ldl  -lutil -lm  -lpython2.7 -Xlinker -export-dynamic -Wl,-O1 -Wl,-Bsymbolic-functions

Project Properties of C++ Eclipse Project titled "test"::

Inside, I had the following C++ Build Settings

GCC C++ Compiler

Command: g++

All options: -I/opt/ros/indigo/include -O0 -g3 -Wall -c -fmessage-length=0

Command line pattern: ${COMMAND} ${FLAGS} ${OUTPUT_FLAG} ${OUTPUT_PREFIX}${OUTPUT} ${INPUTS}

Includes
    include paths: /opt/ros/indigo/include

GCC C Compiler

Command: gcc

All options: -I/opt/ros/indigo/include -I/usr/lib/python2.7/config-i386-linux-gnu -O0 -g3 -Wall -c -fmessage-length=0

Command line pattern: ${COMMAND} ${FLAGS} ${OUTPUT_FLAG} ${OUTPUT_PREFIX}${OUTPUT} ${INPUTS}

Includes
    include paths: /opt/ros/indigo/include
                   /usr/lib/python2.7/config-i386-linux-gnu

GCC C++ Linker

Command: g++

All options: Command line pattern: ${COMMAND} ${FLAGS} ${OUTPUT_FLAG} ${OUTPUT_PREFIX}${OUTPUT} ${INPUTS}

Libraries:

    Libraries(-I): 

    Library search path(-L):

Solution::

Specified the following C++ Build Settings in the Project Properties of C++ Eclipse Project "test"

GCC C++ Compiler

Command: g++

All options: -I/opt/ros/indigo/include -I/usr/include/python2.7 -O0 -g3 -Wall -c -fmessage-length=0

Command line pattern: ${COMMAND} ${FLAGS} ${OUTPUT_FLAG} ${OUTPUT_PREFIX}${OUTPUT} ${INPUTS}

Includes
    include paths: /opt/ros/indigo/include
                   /usr/include/python2.7

GCC C Compiler

Command: gcc

All options: -I/opt/ros/indigo/include -I/usr/include/python2.7 -O0 -g3 -Wall -c -fmessage-length=0

Command line pattern: ${COMMAND} ${FLAGS} ${OUTPUT_FLAG} ${OUTPUT_PREFIX}${OUTPUT} ${INPUTS}

Includes
    include paths: /opt/ros/indigo/include
                   /usr/include/python2.7

GCC C++ Linker

Command: g++

All options: -L/usr/lib/python2.7/config-i386-linux-gnu

Command line pattern: ${COMMAND} ${FLAGS} ${OUTPUT_FLAG} ${OUTPUT_PREFIX}${OUTPUT} ${INPUTS}

Libraries:

    Libraries(-I): python2.7

    Library search path(-L): /usr/lib/python2.7/config-i386-linux-gnu

Result :: Linker errors which resulted previously from the compilation of C++ Eclipse project doesn't occur anymore.

来源：https://stackoverflow.com/questions/27672572/embedding-python-in-c-linking-fails-with-undefined-reference-to-py-initialize

标签

python

python-c-extension