I’m trying to embed Python in C++. This is my Python file (with the name EmbedTest.py):
from __future__ import division class model: def init(self,a,b): self.a = a self.b = b def test_method(a,b): m = model(a,b) m.add(1) print("a: ",a,"b: ",b) return (a+b,a-b,a*b)
This is my C++ file (with the name EmbedTest.cpp and located in the same folder as EmbedTest.py)
#include <Python.h> int main(int argc, char *argv[]) { PyObject *pName, *pModule, *pFunc; PyObject *pArgs, *pValue, *pValue_1, *pValue_2; double sum,diff,prod; double a = atof(argv[1]); double b = atof(argv[2]); Py_Initialize(); pName = PyUnicode_DecodeFSDefault("EmbedTest.py"); pModule = PyImport_Import(pName); Py_DECREF(pName); if(pModule != NULL) { pFunc = PyObject_GetAttrString(pModule,"test_method"); if(pFunc && PyCallable_Check(pFunc)) { pArgs = PyTuple_New(2); pValue_1 = PyFloat_FromDouble(a); pValue_2 = PyFloat_FromDouble(b); if (!pValue_1) { Py_DECREF(pArgs); Py_DECREF(pModule); fprintf(stderr, "Cannot convert argumentn"); return 1; } if (!pValue_2) { Py_DECREF(pArgs); Py_DECREF(pModule); fprintf(stderr, "Cannot convert argumentn"); return 1; } PyTuple_SetItem(pArgs, 0, pValue_1); PyTuple_SetItem(pArgs, 1, pValue_2); pValue = PyObject_CallObject(pFunc, pArgs); Py_DECREF(pArgs); if (pValue != NULL) { sum = PyFloat_AsDouble(PyTuple_GetItem(pValue,0)); diff = PyFloat_AsDouble(PyTuple_GetItem(pValue,1)); prod = PyFloat_AsDouble(PyTuple_GetItem(pValue,2)); printf("a: %f b: %f sum: %f diff: %f prod: %f",a,b,sum,diff,prod); Py_DECREF(pValue); } else { Py_DECREF(pFunc); Py_DECREF(pModule); PyErr_Print(); fprintf(stderr,"Call failedn"); return 1; } } else { if (PyErr_Occurred()) PyErr_Print(); fprintf(stderr, "Cannot find function "%s"n", argv[2]); } Py_XDECREF(pFunc); Py_DECREF(pModule); } else { PyErr_Print(); fprintf(stderr, "Failed to load "%s"n", argv[1]); return 1; } if (Py_FinalizeEx() < 0) { return 120; } return 0; }
Compiling is fine. I use the flags suggested by python3.6-config --cflags
. Hence
gcc -c -I/home/MyFolder/anaconda3/include/python3.6m -Wno-unused-result -Wsign-compare -march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -O3 -pipe -fdebug-prefix-map==/usr/local/src/conda/- -fdebug-prefix-map==/usr/local/src/conda-prefix -fuse-linker-plugin -ffat-lto-objects -flto-partition=none -flto -DNDEBUG -fwrapv -O3 -Wall -Wstrict-prototypes EmbedTest.cpp
works fine.
However, when I try to link, I get a problem. I use the flags suggested by python3.6-config --ldflags
. Hence I try
gcc -o EmbedTest.o -L/home/MyFolder/anaconda3/lib/python3.6/config-3.6m-x86_64-linux-gnu -L/home/MyFolder/anaconda3/lib -lpython3.6m -lpthread -ldl -lutil -lrt -lm -Xlinker -export-dynamic
.
However, I get the following error message:
/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crt1.o: In function `_start': /build/glibc-6V9RKT/glibc-2.19/csu/../sysdeps/x86_64/start.S:118: undefined reference to `main' collect2: error: ld returned 1 exit status
Any idea what goes wrong here?
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Answer
You are not linking the .o file, you are outputing to it.
Change
gcc -o EmbedTest.o -L/home/MyFolder/anaconda3/lib/python3.6/config-3.6m-x86_64-linux-gnu -L/home/MyFolder/anaconda3/lib -lpython3.6m -lpthread -ldl -lutil -lrt -lm -Xlinker -export-dynamic
to
gcc -o EmbedTest EmbedTest.o -L/home/MyFolder/anaconda3/lib/python3.6/config-3.6m-x86_64-linux-gnu -L/home/MyFolder/anaconda3/lib -lpython3.6m -lpthread -ldl -lutil -lrt -lm -Xlinker -export-dynamic