Re: boost.python compilation error (newbie)

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2021-07-11 23:43:00

On 7/9/21 1:09 PM, maths soso via Boost wrote:
> I'm new to boost, I decided installing it by following instructions
> provided at SO:
> https://stackoverflow.com/a/24086375/10213771
> (The only difference is that I used version 1.76)
> Everything went fine, then I decided to compile this C++ file:
> 
> char const* greet(){
>     return "hello, world";}
> #include <boost/python.hpp>
> 
> BOOST_PYTHON_MODULE(hello_ext){
>      using namespace boost::python;
>      def("greet", greet);}
> 
> 
> Since boost.python is not header only library, I needed to link to it on
> compilation, I used the following compile command:
> g++ -I ~/Desktop/boost_1_76_0/ -I /usr/include/python2.7/ main.cpp -o prog
> ~/Desktop/boost_1_76_0/stage/lib/libboost_python27.a
> 
> but I get the following errors:
> /usr/bin/ld:
> /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o: in
> function `_start':
> (.text+0x24): undefined reference to `main'
> /usr/bin/ld:
> /home/sofiane/Desktop/boost_1_76_0/stage/lib/libboost_python27.a(registry.o):
> in function `boost::python::converter::registration::get_class_object()
> const':
> ...
> /usr/bin/ld: function_doc_signature.cpp:(.text+0x1de): undefined reference
> to `PyObject_IsTrue'
> /usr/bin/ld: function_doc_signature.cpp:(.text+0x23e): undefined reference
> to `PyInt_FromLong'
> /usr/bin/ld: function_doc_signature.cpp:(.text+0x28b): undefined reference
> to `PyInt_FromLong'

I'm not a Python expert, but it looks like:

1. You are not linking to the python library that implements the missing 
symbols.
2. You are missing `main` function or the -c compiler option to indicate 
that you want to only compile the file, not link it.