Styjun

I am currently trying to optimize some code I am working on in MATLAB (version R2019a). To compute my results, MATLAB has to compute a certain function a lot of times, slowing down everything. Because of this, I thought writing this function in C and importing this into MATLAB would speed things up a lot. Unfortunately I ran in some troubles by trying to compile the C-code into MATLAB using MEX.

I have used C before, but am certainly not an expert. Anyway I've tested the code in C and it works, the problem lies in trying to compile the code in MATLAB. I am using the GNU Scientific Library (GSL) and should thus include the libraries in compiling with MEX in MATLAB.

The following is a minimal working example leading to the same problems and errors. The C-code looks something like this, saved in MWE.c

#include "mex.h" // The mex library
#include <gsl/gsl_sf_bessel.h> // GSL function

// Define some function, in my case this is somewhat more complicated
double bessel_fun (double *x)

 return gsl_sf_bessel_J0 (*x);


// MEX function needed for compiling in MATLAB
void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])

 //declare variables
 mxArray *x_M, *y_M;
 double *x, *y;

 //associate inputs
 x_M = mxDuplicateArray(prhs[0]);

 //associate outputs
 y_M = plhs[0] = mxCreateDoubleMatrix(1,1,mxREAL);

 // Access variables
 x = mxGetPr(x_M);
 y = mxGetPr(y_M);

 // Save the result in the output variable
 y[0]=bessel_fun(x);

I then compile in MATLAB using

 mex -IC:/MinGW/include -LC:/MinGW/lib -lgsl -lgslcblas MWE.c

Instead of compiling (which does work if I use C-code without including any libraries), MATLAB returns a lot of errors, as follows:

Error using mex
In file included from
C:/ProgramData/MATLAB/SupportPackages/R2019a/3P.instrset/mingw_w64.instrset/x86_64-w64-mingw32/include/stddef.h:7:0,
 from
C:/ProgramData/MATLAB/SupportPackages/R2019a/3P.instrset/mingw_w64.instrset/lib/gcc/x86_64-w64-mingw32/6.3.0/include/stddef.h:1,
 from C:MinGWinclude/stdio.h:68,
 from C:Program FilesMATLABR2019a/extern/include/mex.h:38,
 from C:userpathMWE.c:1:
C:/ProgramData/MATLAB/SupportPackages/R2019a/3P.instrset/mingw_w64.instrset/x86_64-w64-mingw32/include/crtdefs.h:35:19:
error: expected '=', ',', ';', 'asm' or '__attribute__' before 'typedef'
 __MINGW_EXTENSION typedef unsigned __int64 size_t;
 ^~~~~~~
C:/ProgramData/MATLAB/SupportPackages/R2019a/3P.instrset/mingw_w64.instrset/x86_64-w64-mingw32/include/crtdefs.h:45:19:
error: expected '=', ',', ';', 'asm' or '__attribute__' before 'typedef'
 __MINGW_EXTENSION typedef __int64 ssize_t;
 ^~~~~~~
C:/ProgramData/MATLAB/SupportPackages/R2019a/3P.instrset/mingw_w64.instrset/x86_64-w64-mingw32/include/crtdefs.h:52:9:
error: unknown type name 'size_t'
 typedef size_t rsize_t;

[...]

and the same error on different type names.

Does anyone have an idea how to correctly include the libraries when compiling with MEX in MATLAB?

Gotcha. Could you try the following please:

mex -U__MINGW_EXTENSION -IC:/MinGW/include -LC:/MinGW/lib -lgsl -lgslcblas MWE.c