how to debug undefined symbol

[jwuttke]

Say, definition of class A in A.h contains a function f17 that is not implemented in A.cpp.

Binder will pass, pybind11 will pass, compiler will pass, linker will pass - but the Python import statement will fail with a message like

ImportError: my_module.cpython-39-x86_64-linux-gnu.so: undefined symbol: _ZNK1A2a2Ev

How to debug this error? Is there a way to make the error message more explicit? Is there a way to catch this error earlier?

[lyskov]

This is indeed an annoying issue. Simplest way to debug this would to use UNIX nm utility. I usually do something like nm -D --demangle --undefined-only <your-project-lib>.so | grep <primary-namespace>. Also (and sometimes this a bit easier) linking on MacOS will immediately fail if there is unresolved symbols.