Program doesn't swap

**monjai** · 12-02-2008

I am having difficulty with a code in which I have to use selection sorting to sort a list of indexes. The program compiles, but the function I am using to perform the swap doesn't seem to be doing anything. The program is supposed to look at the alphabetical order from the Last Name = lName, to make the list descending order. Any help would be appreciated.

Code:

void sort(PERSON people[], int num)
{
   int pass, trav, min;

   for (pass = 0; pass < num; pass++);
   {
      for (min = pass, trav = pass +1; trav < num; trav++)
      {
         if (strcmp(people[trav].fName, people[min].fName) == 0)
            {
               min = trav;
            } 
      }
         swap(people[trav], people[min]); 

   }
}

void swap (PERSON people1, PERSON people2)
{
   PERSON temp = {"", "", 0, "", {0,0,0}};
printf("bebebe");
   strcpy(temp.fName, people1.fName);
   strcpy(temp.lName, people1.lName);
   temp.Glevel = people1.Glevel;
   strcpy(temp.ssn, people1.ssn);
   temp.bDate.month = people1.bDate.month;
   temp.bDate.day = people1.bDate.day;
   temp.bDate.year = people1.bDate.year;

   strcpy(people1.fName, people2.fName);
   strcpy(people1.lName, people2.lName);
   people1.Glevel = people2.Glevel;
   strcpy(people1.ssn, people2.ssn);
   people1.bDate.month = people2.bDate.month;
   people1.bDate.day = people2.bDate.day;
   people1.bDate.year = people2.bDate.year;

   strcpy(people2.fName, temp.fName);
   strcpy(people2.lName, temp.lName);
   people2.Glevel = temp.Glevel;
   strcpy(people2.ssn, temp.ssn);
   people2.bDate.month = temp.bDate.month;
   people2.bDate.day = temp.bDate.day;
   people2.bDate.year = temp.bDate.year;

}

**~~master5001~~** · 12-02-2008

What does the structure look like?

**Dino** · 12-02-2008

It seems you are passing copies of PERSON on the stack, where you should be passing pointers to PERSON, and then you can use indirection to swap the values.

**~~master5001~~** · 12-02-2008

Ah yes. Nicely done ol' eagle eye.

Code:

void sort(PERSON people[], int num)
{
   int pass, trav, min;

   for (pass = 0; pass < num; pass++);
   {
      for (min = pass, trav = pass +1; trav < num; trav++)
      {
         if (strcmp(people[trav].fName, people[min].fName) == 0)
            {
               min = trav;
            } 
      }
         swap(people + trav, people + min); 

   }
}


void swap (PERSON *people1, PERSON *people2)
{
   PERSON temp = {"", "", 0, "", {0,0,0}};
printf("bebebe");
   strcpy(temp.fName, people1->fName);
   strcpy(temp.lName, people1->lName);
   temp.Glevel = people1->Glevel;
   strcpy(temp.ssn, people1->ssn);
   temp.bDate->month = people1->bDate->month;
   temp.bDate->day = people1->bDate->day;
   temp.bDate->year = people1->bDate->year;

   strcpy(people1->fName, people2->fName);
   strcpy(people1->lName, people2->lName);
   people1->Glevel = people2->Glevel;
   strcpy(people1->ssn, people2->ssn);
   people1->bDate->month = people2->bDate->month;
   people1->bDate->day = people2->bDate->day;
   people1->bDate->year = people2->bDate->year;

   strcpy(people2->fName, temp.fName);
   strcpy(people2->lName, temp.lName);
   people2->Glevel = temp.Glevel;
   strcpy(people2->ssn, temp.ssn);
   people2->bDate->month = temp.bDate->month;
   people2->bDate->day = temp.bDate->day;
   people2->bDate->year = temp.bDate->year;

}

**monjai** · 12-02-2008

I just tired with your suggestion, it came out
error: invalid type argument of `->'
this as errors with all of those you replace

**~~master5001~~** · 12-02-2008

Ooops! Nope. I stupidly deleted one of the parameter types. I bolded my error.

**monjai** · 12-02-2008

Unfortunately, it is still coming up the same errors.

**C_ntua** · 12-02-2008

Err, maybe this:

Code:

void swap (PERSON* people1, PERSON* people2)
{
   PERSON temp = {"", "", 0, "", {0,0,0}};
    printf("bebebe");
   strcpy(temp.fName, people1->fName);
   strcpy(temp.lName, people1->lName);
   temp.Glevel = people1->Glevel;
   strcpy(temp.ssn, people1->.ssn);
   temp.bDate.month = people1->bDate.month;
   temp.bDate.day = people1->bDate.day;
   temp.bDate.year = people1->bDate.year;

   strcpy(people1->fName, people2->fName);
   strcpy(people1->lName, people2->lName);
   people1->Glevel = people2->Glevel;
   strcpy(people1->ssn, people2->ssn);
   people1->bDate.month = people2->bDate.month;
   people1->bDate.day = people2->bDate.day;
   people1->bDate.year = people2->bDate.year;

   strcpy(people2->fName, temp.fName);
   strcpy(people2->lName, temp.lName);
   people2->Glevel = temp.Glevel;
   strcpy(people2->ssn, temp.ssn);
   people2->bDate.month = temp.bDate.month;
   people2->bDate.day = temp.bDate.day;
   people2->bDate.year = temp.bDate.year;

}

Just changing people1 and people2 to pointers and . to -> respectively
edit: missed some dots

**monjai** · 12-02-2008

Good new is it complies, but the result is the same, didn't swap.

**zacs7** · 12-02-2008

Yucky, there's no need to change the values... just move pointers about and leave the internal values of the structures alone!

That's a serious waste of resources copying values around the place.

BTW, is it class time again? Lots of people have been posting stuff about "STUDENTS" and "PEOPLE".

**monjai** · 12-02-2008

Originally Posted by zacs7

Yucky, there's no need to change the values... just move pointers about and leave the internal values of the structures alone!

What do you mean by that?

**zacs7** · 12-02-2008

Have an array of PEOPLE pointers that you move around, ie move the pointers and leave the content alone other than reading the name for sorting that is...

**~~master5001~~** · 12-02-2008

Ah I see... Well it isn't my part that find/replace isn't 100% idiot proof. Especially when I first did find/replace "." with "[color=red]->[/color]" then realized, oops and did a find replace on "temp[color=red]->[/color]" with "temp."

Oh well. I should have done my find/replace a little more carefully -_- In either case, the original code stored data in an array.

I think this would be apt (but I am only guessing since the OP still hasn't posted the structure as I had asked before):

Example:

Code:

/* at the top put this */
#include <string.h>

void swap (PERSON* people1, PERSON* people2)
{
  PERSON temp;

  memcpy(&temp, people1, sizeof temp);
  memcpy(people1, people2, sizeof temp);
  memcpy(people2, &temp);
}

But I am lazy and crazy like that.

**~~master5001~~** · 12-02-2008

zac7's approach would be something like

Example:

Code:

PERSON **sort(PERSON people[], int num)
{
   PERSON **r = malloc(sizeof(*r) * num), *tmp;
   int pass, trav, min;

   if(!r)
      return 0;

   for(pass = 0; pass < num; ++pass)
      r[pass] = people + pass;

   for (pass = 0; pass < num; pass++);
   {
      for (min = pass, trav = pass +1; trav < num; trav++)
      {
         if (strcmp(r[trav]->fName, r[min]->fName) == 0)
            {
               min = trav;
            } 
      }
      
      tmp = r[trav];
      r[trav] = r[min];
      r[min] = tmp;
   }

   return r;
}

**zacs7** · 12-02-2008

Sigh, lets all ignore the proper way to do it...

Code:

#include <stdio.h>

typedef struct people_s
{
   char name[32];
} people_t;

void swap(people_t ** a, people_t ** b);

int main(void)
{
   people_t persons[2] = {{"Adam"}, {"Zac"}};
   people_t * sorted[2];

   
   /* test */
   sorted[0] = &persons[0];
   sorted[1] = &persons[1];

   printf("Before: [&#37;s, %s]\n", sorted[0]->name, sorted[1]->name);

   /* sort */
   swap(&sorted[0], &sorted[1]);

   printf("After: [%s, %s]\n", sorted[0]->name, sorted[1]->name);
   return 0;
}

void swap(people_t ** a, people_t ** b)
{
   people_t * tmp = NULL;

   tmp = *a;
   *a = *b;
   *b = tmp;
}

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