To use Qt with FFTW (Fast Fourier Transfrom in the West) in windows.

  1. download the FFTW pre-compiled *.dll file
    http://www.fftw.org/install/windows.html
  2. extract the zip. Copy the fftw3.h and libfftw3-3.dll and put them into your project folder, the folder same as *.pro file.
  3. in *.pro, add
    LIBS += "$$PWD/libfftw3-3.dll"
  4. in QT creator, on the “projects” column, right click on the project name and select “Add Existing Files…”, choose the fftw.h
  5. in main.cpp, add
    #include "fftw.h"
  6. got to the build directory, usually named as “Build-…..”, you will see “debug” or “release” folders. copy the libfftw3-3.dll and paste it in the “debug” or “release” folder depends on you are debug or release.

The step 6 is very important, without so, the program will not even started, while the compilation is completely normal.