Undefined symbols when linking FFTW & FFTWPP into project with CMAKE on Mac - c++

Question

I am writing a test for a Biquad Filter class I have written in C++, and I am attempting to use to FFTWPP header to simplify the use of the FFTW library. I have successfully built and run the FFTWPP examples, so I can be sure that the FFTW3 library is successfully built and installed on my Mac (running OS Catalina 10.15.5 (19F101)).
I have managed to include the FFTW lib directory into the cmake project definitions, and I have added the appropriate include paths into the CMAKE file:
cmake_minimum_required(VERSION 3.16)
project(IIR)
set(CMAKE_CXX_STANDARD 14)
find_package(Python 3.7 COMPONENTS Development) # Used for MatplotlibPP
include_directories(.)
include_directories(./../../../fftwpp/)
include_directories(./../../../fftw-3.3.8/api/)
include_directories(./../../../matplotlib-cpp/) #Plotting
include_directories(./../../../AudioFile/) #AudiofileIO
include_directories(/usr/local/include) # contains includes for FFTW3
link_directories(.)
link_directories(/usr/local/lib)# contains binary for FFTW3
find_library(
fftw3
NAMES fftw lfftw3 libfftw3
HINTS /usr/local/lib
)
add_executable(IIR
Test_BiquadFilter.cpp)
target_link_libraries(IIR PUBLIC Python fftw3)
However, it appears the linker is failing to link the symbols through the FFTWPP header:
[100%] Linking CXX executable IIR
Undefined symbols for architecture x86_64:
"fftwpp::ThreadBase::ThreadBase()", referenced from:
fftwpp::fftw::fftw(unsigned int, int, unsigned int, unsigned int) in Test_BiquadFilter.cpp.o
"fftwpp::fftw::maxthreads", referenced from:
_main in Test_BiquadFilter.cpp.o
fftwpp::fftw::Setup(std::__1::complex<double>*, std::__1::complex<double>*) in Test_BiquadFilter.cpp.o
"fftwpp::fftw::testseconds", referenced from:
fftwpp::fftw::time(fftw_plan_s*, fftw_plan_s*, std::__1::complex<double>*, std::__1::complex<double>*, unsigned int) in Test_BiquadFilter.cpp.o
"fftwpp::fftw::effort", referenced from:
fftwpp::rcfft1d::Plan(std::__1::complex<double>*, std::__1::complex<double>*) in Test_BiquadFilter.cpp.o
fftwpp::crfft1d::Plan(std::__1::complex<double>*, std::__1::complex<double>*) in Test_BiquadFilter.cpp.o
"fftwpp::fftw::planner", referenced from:
fftwpp::fftw::Setup(std::__1::complex<double>*, std::__1::complex<double>*) in Test_BiquadFilter.cpp.o
"fftwpp::inout", referenced from:
fftwpp::fftw::Setout(std::__1::complex<double>*, std::__1::complex<double>*) in Test_BiquadFilter.cpp.o
"fftwpp::crfft1d::threadtable", referenced from:
fftwpp::crfft1d::lookup(bool, unsigned int) in Test_BiquadFilter.cpp.o
fftwpp::crfft1d::store(bool, fftwpp::threaddata const&) in Test_BiquadFilter.cpp.o
"fftwpp::rcfft1d::threadtable", referenced from:
fftwpp::rcfft1d::lookup(bool, unsigned int) in Test_BiquadFilter.cpp.o
fftwpp::rcfft1d::store(bool, fftwpp::threaddata const&) in Test_BiquadFilter.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Should I be linking the FFTW library against FFTWPP and be building that as its own library, and then link that library against my project?
I know I have probably added some extra parts to the Cmake project unnecessarily, but is my CMake configuration otherwise incorrect for another reason, when linking a library this way?
Many thanks,

Answer 1

The answer to my issues as kindly pointed out by a commenter to the original post, was that I was not linking against FFTWPP.
The solution in this was to add FFTWPP as a library to the project, and add that library to the list of target linked libraries.
link_directories(./../../../fftwpp/)
find_library(
fftw3
NAMES fftw lfftw3 libfftw3
HINTS /usr/local/lib
)
add_library(fftwpp STATIC ./../../../fftwpp/fftw++.cc)
add_executable(IIR
Test_BiquadFilter.cpp)
target_link_libraries(IIR PUBLIC Python fftw3 fftwpp)