Mine

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/* Example worker using a string */
static int worker( double *d_ptr, char *string )
{
    double d = *d_ptr
    return sin(d) + sin(strtod( string, NULL ));
}

/* exported wrapper, all double * arguments, calls the real
** function with whatever data types it expects
*/
int caller(double *x, double *y)
{
    return worker(x,(char *)y);
}