Which is faster, sorting an array of structs or sorting a list of structures C?

Question

I am faced with a challenge. I have data on a linked list of structs. Do l move the data onto an array of structs then sort it using qsort() or do l use merge sort? This is the struct:

struct properties{
    char *path;
    char *name;
    char *extension;
    long int size;
    long unsigned created;
    long unsigned modified;
    long unsigned access;
    int permissions;
};

How you represent "list" in your code? Is it "array" vs. "list" or "qsort" vs. "merge sort" ? — P.P, Jun 16 '15 at 10:47
Do you know how to sort a structure?? How can you move char, long int data on a single array?? It's not possible. — Mr. Perfectionist, Jun 16 '15 at 10:52
The best way to do this is perhaps to implement the linked list as an array, instead of a fully dynamic list. Then sorting becomes trivial. Alternatively, you could consider integrating the linked list with a pointer-based lookup table, so that each item in the linked list can get an index. — Lundin, Jun 16 '15 at 11:05
qsort() available in C can sort an array. It only needs you to specify the sort criterion to be used. You write a comparator function and provide its pointer to qsort(). — Mutai Mwiti, Jun 16 '15 at 11:09
if your properties are malloced separately inside your list (f.e. `struct list {struct properties *prop; struct list *next;};`) or your array you do not have to move so much data , just the pointers. — Peter Miehle, Jun 16 '15 at 11:22
The problem l am faced with is deciding whether to sort data on a linked list or copy the data onto an array then sort it. I find it challenging to decide which would be faster. Of course moving the data to an array incurs a cost. But is that cost worth it? I think sorting an array using qsort() is faster than any method of sorting a linked list for the same data. — Mutai Mwiti, Jun 16 '15 at 11:28

score 3 · Answer 1 · edited May 23 '17 at 10:26

I would create an array of pointers to the structs and sort the pointer array using qsort. Using pointers instad of copying the entire structs will use less memory.

Create a comparator like this:

int propertyComparator(const void *s1, const void* s2) {
    struct property *p1 = (struct property *)s1, *p2 = (struct property *)s2;

    /* compare p1 and p2, below is just an example */
    int result = strcmp(p1->name, p2->name);
    return result;
}

Call it like this:

 struct property *array;
 /* add code to allocate and create array */
 qsort(array, num_elements, sizeof array, propertyComparator);

Edit:

If you want to have a sorted linked list, mergesort is about as fast. Seems it depends on how fragmented the linked list is. See https://stackoverflow.com/a/1525419/646887

The reason I prefer qsort is that it is part of the C lib, so I don't have to write and maintain so much code. And it is always a fast choice.

Thanks you all for your answers. Klas Lindbäck your answer is very informative. Does it mean that l traverse all the elements of the list and get the pointer to each element storing them in the array? — Mutai Mwiti, Jun 16 '15 at 11:40
Yes. And if you don't know the size you need to traverse it twice. First to calculate the size and then to collect the pointers. — Klas Lindbäck, Jun 16 '15 at 11:47

Which is faster, sorting an array of structs or sorting a list of structures C?

1 Answers1