Question

I need to order a array of data structure that contains information relating to a node origin, destination and weight. the problem is not ordered properly, because if two values ​​are equal to array.originNode simply takes the first value you get and not as it should be ordered.

This is how my code does order the structure

0 1 30
1 3 22
2 3 20
3 5 20
3 4 15

Process returned 0 (0x0)   execution time : 0.015 s

Here’s how it should order

0 1 30
1 3 22
2 3 20
3 4 15
3 5 20

I think the problem is the function that I am passing as parameter to qsort, which is not making the correct comparison. How do I change my comparison function to my code sorts the array of struct properly?

this is my full code

#include <stdio.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <unistd.h>

 typedef struct dataNodes{
   int originNode;
   int destinationNode;
   int weight;
   struct dataNodes *next;
} ARRAYS;


  int function (const void * a, const void * b)
{
  return ( *(int*)a - *(int*)b );
}


int main() {
ARRAYS array[6];
int n = 5, i;

array [0].originNode = 3;
array [1].originNode = 3;
array[2].originNode = 1;
array[3].originNode = 0;
array[4].originNode = 2;


array [0].destinationNode = 4 ;
array [1].destinationNode = 5;
array[2].destinationNode = 3;
array[3].destinationNode = 1;
array[4].destinationNode = 3;


array [0].weight = 15;
array [1].weight = 20;
array[2].weight = 22;
array[3].weight = 30;
array[4].weight = 20;


              qsort(array,n,sizeof(array[0]),function);
    for(i=0; i<n; i++)
    {
    printf("%d %d %d\n",array[i].originNode,array[i].destinationNode,
    array[i].weight);
    }
return 0;

}

Answer 1

You need to change your compare function to compare ARRAY records properly. First compare originNode, and if they’re the same compare destinationNode.

int function (const void * a, const void * b)
{
    const ARRAYS *ap = a;
    const ARRAYS *bp = b;
    if( ap->originNode < bp->originNode )
        return -1;
    else if( ap->originNode > bp->originNode )
        return 1;
    else if( ap->destinationNode < bp->destinationNode )
        return -1;
    else if( ap->destinationNode > bp->destinationNode )
        return 1;
    else
        return 0;
 }