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 is `sizeof(int)` and `sizeof(stockItem)`? – dbush Mar 27 '16 at 02:27 — dbush, Mar 27 '16 at 02:27
It just returned the same array, with no changes – Yahya Uddin Mar 27 '16 at 15:17 — Yahya Uddin, Mar 27 '16 at 15:17

Adam Martin · Accepted Answer · 2016-03-27T02:29:42.000

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 '16 at 02:29

answered Mar 27 '16 at 02:22

Adam Martin

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This should be a comment. – Ismail Badawi Mar 27 '16 at 02:24
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)`. – Yahya Uddin Mar 27 '16 at 02:25
2

Yes it should, I posted too early because I have fat fingers on mobile – Adam Martin Mar 27 '16 at 02:25
And now mobile is stripping my links, I give up, link is: http: // goo.gl/ZWwzh0 – Adam Martin Mar 27 '16 at 02:27
And the reason it worked online, is because the struct is actually larger. I just used a smaller version. Editing question now – Yahya Uddin Mar 27 '16 at 02:28

Sorting a array of structs in C

1 Answers1