Question

Hey guys (be forewarned that this question makes me feel n00b so I probably am),

I’m able to dynamically create an array and I’m able to use qsort effectively for a statically created array but am having trouble using qsort on a dynamically created one. I think I’m stumbling on my use of pointers.

struct my_struct {
    FILE *fp;
    int i;
};

So the array contains the above struct and I’d like to sort it by the int value.

Statically, I can do something like this:

struct my_struct array[4];

And sort:

qsort((void *) &array, sizeof(array) / sizeof(struct my_struct), sizeof(struct my_struct), *compare);

—

If I create the array thus:

struct my_struct* = malloc(sizeof(struct process) * 4);

Everything compiles and runs, however execution never goes into the compare function.

Any help would be greatly appreciated

Answer 1

sizeof(array) is (sizeof(struct my_struct) * array_size) for constant-size array, but it’s only pointer size for dynamic one. You have to calculate actual size (one you passed to malloc) yourself and put it into qsort call.