"Segmentation fault" when run python function in C++ code using Cmake

Question

I am learning to embed python code into c++ code. Following the simple example in How to solve the 'Segmentation fault' when hybrid programming of C & Python? and use g++ main.cpp -I/usr/include/python2.7 -L/usr/lib/python2.7 -lpython2.7 to compile the code and run the program, I can get the correct result.

But if I create a "build" folder and using CMake to run the program, it still has segmentation fault.

My CMakeList.txt is like below:

cmake_minimum_required(VERSION 2.8)
project ( pyTest )


if(NOT CMAKE_BUILD_TYPE)
set(CMAKE_BUILD_TYPE "RELEASE")
endif()

string(ASCII 27 Esc)
set(Red "${Esc}[1;31m")
set(ColourReset "${Esc}[m")

if(CMAKE_BUILD_TYPE MATCHES "DEBUG")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x -O0 -g")
MESSAGE(STATUS "${Red}BUILD TYPE: DEBUG${ColourReset}")
else()
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x -O3")
MESSAGE(STATUS "${Red}BUILD TYPE: RELEASE${ColourReset}")
endif()


include_directories( include )
find_package(PythonLibs REQUIRED)
include_directories(${PYTHON_INCLUDE_DIRS})

set(SRC_LIST2 main.cpp)

add_executable( pytest ${SRC_LIST2})
target_link_libraries(pytest ${PYTHON_LIBRARIES})

For convenience, I post my code below:

pytest.py

def Hello():
    print "Hello, world!"

main.cpp

#include <Python.h>

int main()
{

Py_Initialize();
PyRun_SimpleString ("import sys; sys.path.insert(0, 'DIRECTORY_PATH'");
PyObject * pModule = NULL;
PyObject * pFunc   = NULL;

pModule = PyImport_ImportModule("pytest");
pFunc   = PyObject_GetAttrString(pModule, "Hello");
if(pFunc != NULL) {
    PyEval_CallObject(pFunc, NULL);
    Py_Finalize();
}
else {
    printf("pFunc returned NULL\n");
}

return 0;
}

where "DIRECTORY_PATH" is the folder path of my main.cpp file and pytest.py, not the path of "build" folder

When I print out the result of PyImport_ImportModule, it returns 0. I think that means it doesn't get the python model. But my main.cpp and python file are under same directory, I don't know why it cannot get the model...

Can I fix it? Thx!

@Displayname The error is just "Segmentation fault". No other messages...But when I print out the result of PyImport_ImportModule, it returns 0. I think that means it doesn't get the python model. But my main.cpp and python file is under same directory, I don't know why it cannot get the model... — debug_all_the_time
– debug_all_the_time, Commented Jan 13, 2017 at 22:55
The name of your module is pytest, not test. You should have checked the value returned by PyImport_ImportModule before using it. — DYZ
– DYZ, Commented Jan 13, 2017 at 23:46
@DYZ Thanks for pointing out the mistake. I am sorry I just copied the code from the website I referred for convenience. In my code it IS 'pytest'. I just revised in my question. But the problem still exists.... — debug_all_the_time
– debug_all_the_time, Commented Jan 13, 2017 at 23:54
If you compile the program in the DEBUG mode and run under a debugger, you will know on what line does it segfault. That would be very useful. — DYZ
– DYZ, Commented Jan 13, 2017 at 23:59

debug_all_the_time · Accepted Answer · 2017-01-18 19:15:28Z

1

Solved by myself. I should put main.cpp and pytest.py under same directory and use PyRun_SimpleString ("import sys; sys.path.insert(0, 'DIRECTORY_PATH'"); to change 'DIRCTORY_PATH' to current directory that saves main.cpp and pytest.py. (Before I used a wrong dirctory so I got segmentation fault)

answered Jan 18, 2017 at 19:15

debug_all_the_time

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