1. Download precompiled FFTW Version 3.3.5 at http://www.fftw.org/download.html

2. Unzip the file and generate the import library (.lib file) according to the instructions at http://www.fftw.org/install/windows.html

cmd run:

     lib /def:libfftw3f-3.def

     lib /def:libfftw3-3.def

     lib /def:libfftw3l-3.def

Or, you may need to specify the machine explicitly:

     lib /machine:x64 /def:libfftw3f-3.def

     lib /machine:x64 /def:libfftw3-3.def

     lib /machine:x64 /def:libfftw3l-3.def

3. Put the unzipped file into the path

4. Set up the lib of a Qt project:

References:

https://wiki.qt.io/How_to_use_FFTW

https://stackoverflow.com/questions/39675436/how-to-get-fftw-working-on-windows-for-dummies

https://stackoverflow.com/questions/40704437/add-fftw-library-to-qt-project