In some cases it may be advantageous to pass problem-specific data to a user-supplied function through the IMSL C Stat Library interface. This ability can be useful if a user-supplied function requires data that is local to the user's calling function, and the user wants to avoid using global data to allow the user-supplied function to access the data. Functions in IMSL C Stat Library that accept user-supplied functions have an optional argument(s) that will accept an alternative user-supplied function, along with a pointer to the data, that allows user-specified data to be passed to the function. The example below demonstrates this feature using the IMSL C Stat Library function imsls_f_kolmogorov_one and optional argument IMSLS_FCN_W_DATA.
#include <imsls.h>
#include <stdio.h>
float cdf_w_data(float, void *data_ptr);
float cdf(float);
void main()
{
float *statistics=NULL, *diffs = NULL, *x=NULL;
int nobs = 100, nmiss;
float usr_data[] = {0.5, .2886751};
imsls_random_seed_set(123457);
x = imsls_f_random_uniform(nobs, 0);
statistics = imsls_f_kolmogorov_one(cdf, nobs, x,
IMSLS_N_MISSING, &nmiss,
IMSLS_DIFFERENCES, &diffs,
IMSLS_FCN_W_DATA, cdf_w_data, usr_data,
0);
printf("D = %8.4f\n", diffs[0]);
printf("D+ = %8.4f\n", diffs[1]);
printf("D- = %8.4f\n", diffs[2]);
printf("Z = %8.4f\n", statistics[0]);
printf("Prob greater D one sided = %8.4f\n", statistics[1]);
printf("Prob greater D two sided = %8.4f\n", statistics[2]);
printf("N missing = %d\n", nmiss);
}
/*
* User function that accepts additional data in a (void*) pointer.
* This (void*) pointer can be cast to any type and dereferenced to
* get at any sort of data-type or structure that is needed.
* For example, to get at the data in this example
* *((float*)data_ptr) contains the value 0.5
* *((float*)data_ptr+1) contains the value 0.2886751.
*/
float cdf_w_data(float x, void *data_ptr)
{
float mean, std, z;
mean = *((float*)data_ptr);
std = *((float*)data_ptr+1);
z = (x-mean)/std;
return(imsls_f_normal_cdf(z));
}
/* Dummy function to satisfy C prototypes. */
float cdf(float x)
{
return;
}
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