How can I pass a variable to a function here?

Question

I use qsort from stdlib.h,

void qsort (void* base, size_t num, size_t size,
            int (*compar)(const void*,const void*));

in the following way:

void myfun (float *arr, int n, float c) // value of c is changeable
{
...// some code
qsort(float *arr, n, sizeof(float), compareme);
...// some code
}

with

int compareme (const void * a, const void * b)
{
  float tmp = f((float*)a,  (float*)b, c );  // f is some function, and how can I pass c here?
  if (tmp < 0) return -1;
  if (tmp == 0) return 0;
  if (tmp > 0) return 1;
}

how can I make c usable in compareme here?

Thanks!

Answer 1

Many resort to using a (nasty) global variable.

It is too bad that qsort() doesn't include an extra void pointer argument that is just passed to the user-supplied compar() function. I ended up writing my own qsort() to overcome this limitation.

Prototype:

int myQsort(
    void  *arrayBase,
    size_t elements,
    size_t elementSize,
    int(*compar)(const void *, const void *, void *callerArg),
    void *callerArg
    ); 

This allows me to pass all kinds of structures (cast to void *) to my compar() fn.