fftw library, undefined reference to `fftwf_*' - c++11

Question

Well, it's a very strange error I met.
When I try to compile my program with the fftw library by the command:
g++ -std=c++11 -o main main.cpp BFSCcommandlineParser.cpp BFSCframe.cpp BFSCgeometry.cpp ImageIO.cpp -lfftw3 -lm
... I get this:
/tmp/cczUuTb0.o: In function `fftw_prog::fftw_prog(char const*)':
main.cpp:(.text._ZN9fftw_progC2EPKc[_ZN9fftw_progC5EPKc]+0x5c): undefined reference to `fftwf_import_wisdom_from_file'
/tmp/cczUuTb0.o: In function `fftw_prog::~fftw_prog()':
main.cpp:(.text._ZN9fftw_progD2Ev[_ZN9fftw_progD5Ev]+0x31): undefined reference to `fftwf_export_wisdom_to_file'
/tmp/cczUuTb0.o: In function `fft<2, float, std::complex<float> >::fft(tensor<int, 2ul>, bool)':
main.cpp:(.text._ZN3fftILi2EfSt7complexIfEEC2E6tensorIiLm2EEb[_ZN3fftILi2EfSt7complexIfEEC5E6tensorIiLm2EEb]+0xcf): undefined reference to `fftwf_plan_dft_r2c'
main.cpp:(.text._ZN3fftILi2EfSt7complexIfEEC2E6tensorIiLm2EEb[_ZN3fftILi2EfSt7complexIfEEC5E6tensorIiLm2EEb]+0x111): undefined reference to `fftwf_plan_dft_c2r'
/tmp/cczUuTb0.o: In function `fft<2, float, std::complex<float> >::~fft()':
main.cpp:(.text._ZN3fftILi2EfSt7complexIfEED2Ev[_ZN3fftILi2EfSt7complexIfEED5Ev]+0x25): undefined reference to `fftwf_free'
main.cpp:(.text._ZN3fftILi2EfSt7complexIfEED2Ev[_ZN3fftILi2EfSt7complexIfEED5Ev]+0x35): undefined reference to `fftwf_destroy_plan'
main.cpp:(.text._ZN3fftILi2EfSt7complexIfEED2Ev[_ZN3fftILi2EfSt7complexIfEED5Ev]+0x45): undefined reference to `fftwf_destroy_plan'
/tmp/cczUuTb0.o: In function `fft<2, float, std::complex<float> >::r2F()':
main.cpp:(.text._ZN3fftILi2EfSt7complexIfEE3r2FEv[_ZN3fftILi2EfSt7complexIfEE3r2FEv]+0x25): undefined reference to `fftwf_execute'
/tmp/cczUuTb0.o: In function `fft<2, float, std::complex<float> >::F2r()':
main.cpp:(.text._ZN3fftILi2EfSt7complexIfEE3F2rEv[_ZN3fftILi2EfSt7complexIfEE3F2rEv]+0x35): undefined reference to `fftwf_execute'
collect2: error: ld returned 1 exit status
I thought it could be a problem of fftw itself, so I tested the library with a proram, and it worked. That means that it's not so.
The following code is a template from my file which is the only one in my project that uses fftw.
template <int N, typename rT, typename FT>
inline fft<N,rT,FT>::~fft() {
if (data != 0) {
if (Precision<rT>::IsFloat) {
fftwf_free((fftwf_complex *)data);
fftwf_destroy_plan((fftwf_plan_s*) r2Fplan);
fftwf_destroy_plan((fftwf_plan_s*) F2rplan);
}
else {
fftw_free((fftw_complex *)data);
fftw_destroy_plan((fftw_plan_s*) r2Fplan);
fftw_destroy_plan((fftw_plan_s*) F2rplan);
}
}
}

Answer 1

For single precision (float) you need to link the libfftwf library, for double precision (double) you need the libfftw library. I would guess you are just linking the latter and not the former. For gcc et al the command line needs to contain -lfftw3 -lfftw3f if you want both double and single precision support.