mex compilation error running fftw3 library

Hi

I need to compile a c++ code as a mex file. It uses the library fftw3. For now I am just trying to run a simple fftw3 example code dowanloaded from

 https://github.com/undees/fftw-example/blob/master/fftw_example.c

If I run it from the terminal it compiles the code:

 gcc -Iusr/local/include/ -L/usr/local/lib -lfftw3 -pat_to_fftw_example.c

But if i run the same in matlab:

 mex -Iusr/local/include/ -L/usr/local/lib -lfftw3 -pat_to_fftw_example.c

I get this error:

 Error using mex

 ld: warning: directory not found for option '-L/usr/local/opt/llvm/4.0.0_1' 
 Undefined symbols for architecture x86_64:

 "_mexFunction", referenced from: -exported_symbol[s_list] command line option

 ld: symbol(s) not found for architecture x86_64

 clang: error: linker command failed with exit code 1 (use -v to see invocation)

Anybody knows how to solve it?

Thanks

Answer 1

[Aylin]

The "Undefined symbols for architecture..._mexFunction" error is usually caused by a missing mexFunction function.

In C/C++ applications, the program entry point is usually defined using the main function which has a specific signature:

int main() {...}
int main( int argc, char *argv[] ) {...}

Similarly, the entry point in a MATLAB MEX file is defined using the mexFunction:

void mexFunction( int nlhs, mxArray *plhs[], int prhs, const mxArray *prhs[] ) {...}

https://www.mathworks.com/help/matlab/apiref/mexfunction.html

If you add a mexFunction to your 'fftw_example.c', it can be compiled with the mex command. See some of the mex examples for more information:

https://www.mathworks.com/help/matlab/matlab_external/standalone-example.html

The mex function reference page and the MATLAB matrix API reference could also help with this.