Sorting a array of structs in C

Question

I have a array of struct, which I wish to sort in ascending order.

After quite a lot of research on Stack Overflow, I found sorting members of structure array.

Therefore I have the following code:

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

typedef struct StockItem {
    int unitPrice;
    // ...
} stockItem;

int comparePrice(const void* a, const void* b)
{
    stockItem *stockItem1 = (stockItem *) a;
    stockItem *stockItem2 = (stockItem *) b;
    return stockItem1->unitPrice - stockItem2->unitPrice;
}

int main() {
    stockItem stockItem1;
    stockItem1.unitPrice = 15;

    stockItem stockItem2;
    stockItem2.unitPrice = 41;

    stockItem stockItem3;
    stockItem3.unitPrice = 25;

    stockItem stockItems[3] = {stockItem1, stockItem2, stockItem3};
    int size = 3;

    qsort(stockItems, (size_t) size, sizeof(int), comparePrice);

    printf("\n");
    for (int i = 0; i < size; i++) {
        printf("%d\n", stockItems[i].unitPrice);
    }

    return 0;
}

However, this doesn't seem to sort the array.

What output do you get?

Adam Martin
– Adam Martin

2016-03-27 02:17:43 +00:00
Commented Mar 27, 2016 at 2:17 — Adam Martin
– Adam Martin, Commented Mar 27, 2016 at 2:17
What is sizeof(int) and sizeof(stockItem)?

dbush
– dbush

2016-03-27 02:27:00 +00:00
Commented Mar 27, 2016 at 2:27 — dbush
– dbush, Commented Mar 27, 2016 at 2:27
It just returned the same array, with no changes

Yahya Uddin
– Yahya Uddin

2016-03-27 15:17:05 +00:00
Commented Mar 27, 2016 at 15:17 — Yahya Uddin
– Yahya Uddin, Commented Mar 27, 2016 at 15:17

Adam Martin · Accepted Answer · 2016-03-27 02:29:42Z

4

That's weird. The only thing I can see is that you should be using sizeof(stockItem), not int, but that shouldn't matter unless your system has weird alignment. Also the cast to size_t on size isn't necessary, but that definitely doesn't matter.

Edit: I tried to add a link to the code working online, but it I'm bad links. Basically, the struct alignment isn't guaranteed unless you use packing.

edited Mar 27, 2016 at 2:29

answered Mar 27, 2016 at 2:22

Adam Martin

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5 Comments

Ismail Badawi Over a year ago

This should be a comment.

Yahya Uddin Over a year ago

That's actually the answer! Try rewording your post to be more suited as an answer. I used sizeof(int), where I should have used sizeof(stockItem).

Adam Martin Over a year ago

Yes it should, I posted too early because I have fat fingers on mobile

Adam Martin Over a year ago

And now mobile is stripping my links, I give up, link is: http: // goo.gl/ZWwzh0

Yahya Uddin Over a year ago

And the reason it worked online, is because the struct is actually larger. I just used a smaller version. Editing question now

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