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Running python script from c++ code and use pythons output in c++

I'm have a C++ program that is pretty far developed to do it's own job and now we'd like to add an addition functionality to it and we thought that making said functionality in Python and then calling that python with required inputs from the C++ when needed would be the best way to go as it keeps them separated and allows us to use this python script from elsewhere too.
As a first step I decided to try to make a test program to see how this would work and seems like it was a good idea because I can't get it to work.
How do I run separate python from c++?
I have tried following this guide and while it seems good it doesn't give any information on what compiler options should I run this with?
I have two files, cpp.cpp and python.py
This is my cpp.cpp file:
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <ncurses.h>
#include <Python.h>
using namespace std;
int main() {
std::cout << "C++ program started!\n";
char filename[] = "python.py";
FILE* fp;
Py_Initialize();
fp = _Py_fopen(filename, "r");
PyRun_SimpleFile(fp, filename);
Py_Finalize();
std::cout << "C++ program is ending!\n";
return 0;
}
and my python file is just two printf line:
#print('External Python program running...')
#print('Hello World from Python program')
I then try to compile this, give it all the includes it seems to want and then execute the output file:
g++ -I . -I /home/ahomm/python3.6/Include -I /home/ahomm/python3.6/release cpp.cpp && ./a.out
This is the output I get:
/tmp/cccQsh1p.o: In function `main':
cpp.cpp:(.text+0x3f): undefined reference to `Py_Initialize'
cpp.cpp:(.text+0x52): undefined reference to `_Py_fopen'
cpp.cpp:(.text+0x70): undefined reference to `PyRun_SimpleFileExFlags'
cpp.cpp:(.text+0x75): undefined reference to `Py_Finalize'
collect2: error: ld returned 1 exit status
What am I missing? is just something just a little or completely wrong?
cpp and py files and located in the same directory.
And how do I then read the output of python in C++? Haven't even got to that yet...

You have to link your code with libpython3.x.a/python3.x.lib (x - version of python you use). Which file to link: *.a or *.lib depends of your OS. The files are available with python distribution.
Here is a code with cmake that works for me:
cmake_minimum_required(VERSION 2.8.9)
project (embpy)
add_executable(embpy embpy.cpp)
target_include_directories(embpy PRIVATE /path-to-python/Python38/include/python3.8)
target_link_libraries(embpy /path-to-python/Python38/lib/libpython3.8.a)
the embpy.cpp is the same as yours

Figured it out myself then, the problem was incomplete compiler arguments.
This is what I got it to works with:
g++ -fPIC $(python3.6-config --cflags) cpp.cpp $(python3.6-config --ldflags)
the key missing parts were $(python3.6-config --cflags) before and $(python3.6-config --ldflags) after the file that was to be compiled. The first one gives g++ the compile options and the latter gives the flags for linking.
Found the solution from python docs, part 1.6.

Can't link Python libraries inside C program

I want to run a basic python script inside a C program using Eclipse. This is the code:
#include <Python.h>
int main(int argc, char *argv[])
{
Py_SetProgramName(argv[0]); /* optional but recommended */
Py_Initialize();
PyRun_SimpleString("from time import time,ctime\n"
"print 'Today is',ctime(time())\n");
Py_Finalize();
return 0;
}
I am trying to link to several shared libraries like libpython2.7.so in Eclipse linker settings but I always get this error:
Invoking: GCC C Linker
gcc -L/usr/lib/x86_64-linux-gnu/ -o "Test" ./src/Test.o -llibpython2.7
/usr/bin/x86_64-linux-gnu-ld: cannot find -llibpython2.7
collect2: error: ld returned 1 exit status
I can't find any tutorial with the name of the lib that should be linked.

Typically -l doesn't require the lib prefix or the .so suffix...
Try using -lpython2.7 instead of -llibpython2.7.

Qt: Undefined symbols when trying to use python.h in qt

I am doing some tiny work with Qt on Mac. I need to call a python function in my main function. But when I try to call Py_initialize() as everyone said, compiler throws a error like this:
Undefined symbols for architecture x86_64:
"_Py_Initialize", referenced from:
_main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see
invocation)
make: *** [video.app/Contents/MacOS/video] Error 1
07:48:07: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project video (kit: Desktop Qt 5.8.0
clang 64bit)
When executing step "Make"
My code is trivial and there should not be anything weird about this. Here it is:
// bunch of headers
#include <python2.7/Python.h>
using namespace std;
int main(int argc, char *argv[])
{
Py_Initialize();
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
QQmlComponent component(&engine, QUrl(QStringLiteral("qrc:///main.qml")));
QObject *object = component.create();
QObject *mainForm = object->findChild<QObject*>("mainForm");
SignalNexus sn;
QObject::connect(mainForm, SIGNAL(populateToken(QString)), &sn, SLOT(pushToPipe(QString)));
QObject::connect(&sn, SIGNAL(populateResult(QVariant, QVariant)), mainForm, SLOT(handleResult(QVariant, QVariant)));
return app.exec();
}
When I comment the Py_initalize() line, everything works fine. I figure that this is something to do with OSx. But I really don't know how to fix this thing. Help needed.

Change your include line to this
// bunch of headers
#include <Python/Python.h>
using namespace std;
int main(int argc, char *argv[])
{
Py_Initialize();

possible to compile python.exe without Visual Studio, with MinGw

I am trying to achieve things laid out on this page:
https://blogs.msdn.microsoft.com/pythonengineering/2016/04/26/cpython-embeddable-zip-file/
The code I am trying to compile is just this:
#include "Python.h"
int
wmain(int argc, wchar_t **argv)
{
return Py_Main(argc, argv);
}
In VisualStudio 15 I have to add the python/include and link to the python libs directories in the project and also add:
#include "stdafx.h"
and then it compiles and works fine. I'm just curious, is it possible to do this with mingw, or another open source C/C++ compiler?
If I place a file my_python.cpp which contains the following:
#include "include/Python.h"
int
wmain(int argc, wchar_t **argv)
{
return Py_Main(argc, argv);
}
in the root directory of a fresh 32-bit python 3.5 install (windows 7 x64), cd to that directory and try to run:
gcc my_python.cpp -Llibs -lpython35 -o my_python.exe
I get this error:
c:/mingw/bin/../lib/gcc/mingw32/5.3.0/../../../libmingw32.a(main.o):(.text.startup+0xa0): undefined reference to `WinMain#16'
Any way to fix this, get it running without Visual Studio?

The error is unrelated to Python. wmain is Visual Studio specific. GCC does not treat wmain as entry point, it just sits there as a function which never gets called.
GCC requires main or WinMain as entry point. If neither of those entry points is found, then the compiler will complain. So let's just use main as entry point.
Py_Main presumably expects wide character string input. CommandLineToArgvW will always provide that. Example:
#include <Windows.h>
#include "include/Python.h"
int main()
{
int argc;
wchar_t** argv = CommandLineToArgvW( GetCommandLineW(), &argc );
return Py_Main(argc, argv);
}
If you still get the same error, just provide WinMain entry point to make it happy
#include <Windows.h>
#include "include/Python.h"
int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
{
int argc;
wchar_t** argv = CommandLineToArgvW( GetCommandLineW(), &argc );
return Py_Main(argc, argv);
}
Also note, *.lib files are usually for Visual Studio. GCC version expects library names with *.a extension.

How can I link python embedded in a c/c++ application

I would like to use python embedded in a c++ application.
Here is my code:
#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 have included in the c:\log\python27\include to get Python.h and also c:\log\python27\libs to have the corresponding linked library of python which is installed in c:\log\python27
It's compiling but not linking... Why?
I always have followings errors:
main.o:main.cpp:(.text+0x17): undefined reference to `_imp__Py_SetProgramName'
main.o:main.cpp:(.text+0x1e): undefined reference to `_imp__Py_Initialize'
main.o:main.cpp:(.text+0x34): undefined reference to `_imp__PyRun_SimpleStringFlags'
main.o:main.cpp:(.text+0x3b): undefined reference to `_imp__Py_Finalize'

You can use this simple command if you are using python3.5
g++ test.cpp -I/usr/include/python3.5 -lpython3.5m -o call_function
depending where your libraries are!