Linking FFTW into Matlab Mex file

I am trying to run FFTW code in a mex file. This is strictly for the purpose of development and testing. After some googling, I see that oth开发者_如何转开发ers have tried to do something similar and have had related problems, but I have not found any solutions. When attempting to run the mex file, Matlab tells me:

??? Error using ==> chirpTransform.mxCta Invalid MEX-file '\removed\my\directory\+chirpTransform\mxCta.mexw32': The specified procedure could not be found.

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I am using gnumex with MinGW to build the mex file because LCC seems to have some issues. I have tried using the 32 bit DLL from the FFTW site (http://www.fftw.org/install/windows.html). I have tried using the fftwf3.dll in the Matlab 2009b bin directory. I built the dll from source using Msys/MinGW. In all cases, the results are the same. In all cases I did the following to generate the lib file.

c:\gnumex\mexdlltool.exe -d libfftw3f-3.def -D libfftw3f-3.dll -l libfftw3f.lib --as C:\MinGW\bin\as.exe

I also tried using the visual studio lib.exe tool and experimented with various mexdlltool flags.

It appears that I can directly call functions in the fftwf3-3.dll using Matlab's loadlibrary functionality. Since the DLL appears not to be the problem, I tried building a static version of fftwf3 and linking it directly into the mex file. I got the same results! If I remove the FFTW code, the mex file runs fine. I have just about given up at this point, and I am tyring to come up with alternative methods of testing.

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I've run into this issue with other mex functions. In my experience, it typically means that there is a dependency issue. Some dependency is not located.

Here is a link to TMW's documentation on this issue: Invalid MEX-File Error

Give it a read, and then try using dependency walker to diagnose the problem.

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It's been a long time, and my setup has changed, but this works for me now. I suspect hoogamaphone was right. I probably didn't have the fftw dll in the same directory as the mex dll (and it wasn't in my path). In fact, 64 bit Matlab 2016a still gives you a warning about not being able to find the mex file when, in fact, it's a dependency that's missing.

My current setup is using the Visual Studio 2013 C++ compiler by default. As mentioned on the fftw web site, you need to generate a lib file for linking. You can run the Visual Studio command prompt from a regular command prompt like so:

"%VS120COMNTOOLS%VsDevCmd.bat"

Then run the following in the directory with the def file.

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

And compile.

mex mxCta.c cta.c -I../fftw -L../fftw -llibfftw3f-3.lib

Perhaps another possibility is that gnumex introduced some dependency into the mex dll. I no longer recall whether I had used gnumex successfully testing other code. When using cygwin, if you don't use the mingw compiler (x86_64-w64-mingw32-gcc), you'll end up with a dependency on the cygwin1.dll.

Finally, if you use more than one compiler, make sure all the compiler flags are the same (same function calling conventions, ABI, etc). Also, Mathworks has changed the mex build procedure. In a recent project, I copied mexconfig.xml to my local directory from

C:\Users\myuser\AppData\Roaming\MathWorks\MATLAB\R2016a\mex_C_win64.xml

and edited the compiler flags like so:

COMPFLAGS="/Zp8 /GR /W3 /EHs /nologo /MD /Gz /TC"

If you use a custom build file, use the -f option.

mex mxCustom.c custom.lib -f mexconfig.xml