Undefined reference to `PyString_FromString'

Question

I have this C code:

... [SNIP] ...
for(Node = Plugin.Head; Node != NULL; Node = Node->Next) {
    //Create new python sub-interpreter
    Node->Interpreter = Py_NewInterpreter();
    if(Node->Interpreter == NULL) {
        Die("Py_NewInterpreter() failed");
    }

    //Create path to plugins main source file
    snprintf(Filename, FILENAME_MAX, "%s/main.py", Node->File);

    //Convert filename to python string
    PFilename = PyString_FromString(Filename);
    if(PFilename == NULL) {
        Die("PyString_FromString(%s) failed", Filename);
    }

    //Import plugin main source file
    PModule = PyImport_Import(PFilename);
    if(PModule == NULL) {
        Die("PyImport_Import(%s) failed", Filename);
    }

    //Deallocate filename
    Py_DECREF(PFilename);

    //Get reference to onLoad function from module
    PFunction = PyObject_GetAttrString(PModule, "onLoad");
    if(PFunction == NULL) {
        Die("PyObject_GetAttrString() failed");
    }
}
... [SNIP] ...

Which gives this error when compiled:

/tmp/ccXNmyPy.o: In function `LoadPlugins':
/home/alex/Code/Scribe/Scribe.c:693: undefined reference to `PyString_FromString'
collect2: error: ld returned 1 exit status

Python.h is included at the top of the source file.

I'm compiling with:

gcc -funwind-tables -rdynamic -I /usr/include/python2.7/ -g -o Scribe Scribe.c -lcurses `python-config --cflags` `python-config --ldflags` -Wall

I'm basing the code on the Python C-Api docs, from here:

http://docs.python.org/2/c-api/

Specifically:

http://docs.python.org/2/c-api/string.html?highlight=pystring_fromstring#PyString_FromString

I have no idea why this is happening, halp? =c

Answer 1

Solved it, thanks to some help from martineau.

Turns out the python-config --cflags and python-config --ldflags lines generated flags that included the python3.3 include directory in the search path and linked the python3.3 lib.

Naturally python3.3 doesn't work so well with python2.7 C-API, which is what caused this problem.

My solution was to copy the output of python-config --cflags and python-config --ldflags and edit it so it included python2.7 instead of python3.3m:

-I/usr/include/python2.7 -I/usr/include/python2.7 -Wno-unused-result -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 -D_FORTIFY_SOURCE=2 -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 -D_FORTIFY_SOURCE=2

-lpthread -ldl -lutil -lm -lpython2.7 -Xlinker -export-dynamic

Instead of:

-I/usr/include/python3.3m -I/usr/include/python3.3m -Wno-unused-result -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 -D_FORTIFY_SOURCE=2 -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 -D_FORTIFY_SOURCE=2

-lpthread -ldl -lutil -lm -lpython3.3m -Xlinker -export-dynamic

Answer 2

The order of the libraries is important. Try compiling with -lpython2.7 appearing last in the library list.