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More qsort help

Posted on 2007-10-15
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Last Modified: 2008-02-07
I am still having problems with my qsort function.  I am not receiving any errors, but it is not sorting by the percentage in descending order.  Actually, it does not appear to be sorting at all.
Here is my function:
int SortPercent (const void* ptrpercent1, const void* ptrpercent2){
      VEHICLE* ptrp1 = (VEHICLE*) ptrpercent1;
      VEHICLE* ptrp2 = (VEHICLE*) ptrpercent2;
      if (ptrp1->percent > ptrp2->percent)
            return -1;
      if (ptrp1->percent > ptrp2->percent)
            return 1;
return 0;
}

Here is how I am trying to call it in main:
// I assume I need to call the qsort function before "DisplayVehicleMatch"?
qsort ((void*)vehRec, vehCount, sizeof (VEHICLE), SortPercent);
DisplayVehicleMatch (vehRec, request, vehCount);

Here is my DisplayVehicleMatch function:
void DisplayVehicleMatch (VEHICLE vehRec[], VEHICLE request, int limit) {

      for (int i =0; i < limit; i++){
            //set up percentage calculations
             vehRec[i].percent = vehRec[i].count/12.*100;
            //print results of query
                  if (vehRec[i].count > 0)
                  {

                        cout << "Make: " <<  vehRec[i].make;
                        cout << endl << "Model: " << vehRec[i].model;
                        cout << endl << "Count: " << vehRec[i].count;
                        cout << endl  << fixed << setprecision(2)  << "Percent: " << vehRec[i].percent << "%";
                        cout << endl << "_________________________________\n\n";
                  }
      }
}

Any advice would be greatly appreciated.
0
Comment
Question by:gndcdosps
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7 Comments
 
LVL 22

Expert Comment

by:JimBrandley
ID: 20082359
The problem is here:
int SortPercent (const void* ptrpercent1, const void* ptrpercent2){
      VEHICLE* ptrp1 = (VEHICLE*) ptrpercent1;
      VEHICLE* ptrp2 = (VEHICLE*) ptrpercent2;
      if (ptrp1->percent > ptrp2->percent)
            return -1;
      if (ptrp1->percent > ptrp2->percent)
            return 1;
return 0;

Both are looking for ptrp1->percent > ptrp2->percent. Change the first to:
ptrp1->percent < ptrp2->percent

Jim
0
 

Author Comment

by:gndcdosps
ID: 20082425
Thanks, but no luck yet... Still no errors.  I do not think I am calling it right.  How do I point this function and tell it that it needs to point to the precent field to sort?  I have not worked with pointers before, so this is all new to me.  Let me know if you need to see any more of my code.
0
 
LVL 22

Expert Comment

by:JimBrandley
ID: 20082432
Can you post qsort?

Jim
0
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Author Comment

by:gndcdosps
ID: 20082512
Well, I am doing the comparison in the function SortPercent:
int SortPercent (const void* ptrpercent1, const void* ptrpercent2){
      VEHICLE* ptrp1 = (VEHICLE*) ptrpercent1;
      VEHICLE* ptrp2 = (VEHICLE*) ptrpercent2;
      if (ptrp1->percent < ptrp2->percent)
            return -1;
      if (ptrp1->percent > ptrp2->percent)
            return 1;
       return 0;

}
Then  in my main I am calling the qsort function, as its prototype specified in my text:
qsort ((void*)vehRec, vehCount, sizeof (VEHICLE), SortPercent);
// Next I call the display
DisplayVehicleMatch (vehRec, request, vehCount);

I am sure my my problem has something to do with not telling my program which vehRec structure I am wanting to point to.  I just do not understand how?
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LVL 22

Accepted Solution

by:
JimBrandley earned 2000 total points
ID: 20082749
Here's another possibility. Inside DisplayVehicleMatch, you set:
vehRec[i].percent = vehRec[i].count/12.*100;

What does vehRec[i].percent  contain before this? Was it not already set befor the qsort invocation?

Jim
0
 

Author Comment

by:gndcdosps
ID: 20082788
THANKS A BUCH!  THAT DID THE TRICK!
0
 
LVL 22

Expert Comment

by:JimBrandley
ID: 20082795
My pleasure.  Good luck,

Jim
0

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