Thread: QSort on structure array

I have a structure array that is created in a function locally, in order to copy to it the contents of a linked list so that they can be sorted and then printed.

How do I implement qsort in this case?

Code:

/* Initialize record structure for each soldier */
struct record {
	long int aa;
	char firstname[20];
	char lastname[30];
	struct sdate datein;
	struct sdate dateout;
	int freedays;
	int servicedays;
} soldiers;

/* Initialize nodes for linked list */
struct node {
	struct record	soldier;
	struct node*	next;
};

And then in the function that is called when we want to sort the linked list basied on servicedays...

Code:

void servicequeue(struct node* head, int number, int countrec)
{
	int i;
	struct record queue[countrec];
	struct node* current = head;
	
	for (i=0;i<countrec;i++) {
		queue[i] = current->soldier;
		current = current->next;
	}
	
	qsort((void *) queue, countrec, sizeof (struct record), compare(queue));
	
	printf ("Yphresia prepei na kanoun oi parakatw:\n");
	for (i=0;i<number;i++) {
		printf ("&#37;s %s\n", queue[i].firstname, queue[i].lastname);
	}
}

int compare(struct record queue, const void *p1, const void *p2)
{
	return (((queue*)p1)->servicedays - ((queue*)p2)->servicedays);
}

...which obviously doesn't work, and it was a long shot based on a suggestion in another thread. Anyone able to help me get it right?

The example I saw didn't have any struct element in the compare function because the structure was globally declared. What should I do now that it's declared locally? I only need one tiny correction.

countrec is the number of records in the linkedlist, number is how many elements we want to show from the top after we sort.

For one thing the signature of the compare function appears to be wrong.

qsort reference

From what I see the struct is declared globally (the array is local). The name of your struct should do just as good as int in the example.

That is, the compare function is supposed to compare any two instances of this struct, not any two elements in a particular array.

If you still have trouble try creating a minimal compilable example (that can produce your errors), by removing stuff like sdate and anything else that is not essential to the problem.

Depends on how you implement the bubble-sort. Does it takes a compare function that takes two void pointers and returns an int, so you can quickly change what can be sorted?