mex-file crashes MATLAB in for loop

When I call the mex function (which was created using my c code below) in a for loop, it crashes Matlab after several runs. Do you see anything that is wrong with my code?

Additional Info:

• The Arb library depends on the GMP, MPFR and FLINT c libraries.
• I installed a recent version of mingw64 compiler via msys2.
• I ran setenv('MW_MINGW64_LOC', 'C:\msys64\mingw64') to get the mex command to work.
• Disclaimer: What I did to create the c code and get the mex command to run was extremely heuristic and trial-and-error-like, since I don't know much about C, compilers, etc.

#include <mex.h>
#include <matrix.h>
#include "arb.h"
#include "arb_hypgeom.h"

void mexFunction(
    int nlhs, mxArray *plhs[],
    int nrhs, const mxArray *prhs[])
{	
	double *a_double;
	double *b_double;
	double *z_double;
	double *prec_double;
	
	a_double = mxGetDoubles(prhs[0]);
	b_double = mxGetDoubles(prhs[1]);
	z_double = mxGetDoubles(prhs[2]);
	prec_double = mxGetDoubles(prhs[3]);
	
	/* arb_t represents an interval [m±r]≡[m−r,m+r] */
	arb_t a, b, z, r;	
 	arb_init(a);
	arb_init(b);
	arb_init(z);
	arb_init(r);
 	arb_set_d(a, *a_double);
	arb_set_d(b, *b_double);
	arb_set_d(z, *z_double);
 
	/* Set precision parameter*/
	slong prec;
	prec = *prec_double;
        
        /* THIS IS THE ONLY FUNCTION I ACTUALLY WANT FROM ARB LIBRARY TO USE IN MATLAB.
        (It corresponds to the kummerU function in Matlab) */
	arb_hypgeom_u(r, a, b, z, prec);
	
	char *y;
	/* This converts the interval arb_t, to a string which is just the midpoint */
	y = arb_get_str(r,1000,ARB_STR_NO_RADIUS);

	/* output the string y */
	plhs[0] = mxCreateString(y);
	
	mxFree(a_double);
	mxFree(b_double);
	mxFree(z_double);
	mxFree(prec_double);
	
	arb_clear(a);
	arb_clear(b);
	arb_clear(z);
	arb_clear(r);
	
	flint_cleanup();
	
	return;
}

Answer 1

[Bruno Luong]

Those are wrong, you should not Free the pointers that you are not Malloc.

	mxFree(a_double);
	mxFree(b_double);
	mxFree(z_double);
	mxFree(prec_double);

[Michael Stollenwerk]

Thank you very much!