CODEWITHSUNDEEP
csortingfunction-pointers
snapdogfall
snapdogfall

Reputation: 45

calling a quick sort function with the comparison function as a parameter

This is probably a very basic question, but I'm having trouble with understanding pointers thoroughly. In my program below, in the main method, I'm just wondering what the right way to test my Qsort function is. Thanks in advance!

#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>



void swap(void *v[], int i, int j)
{
    void *temp;
    temp = v[i];
    v[i] = v[j];
    v[j]=temp;
}

int cmp1 (void *first_arg,  void *second_arg)
{
    int first = *(int *)first_arg;
    int second = *(int *)second_arg;
    if ( first < second )
    {
        return -1;
    }
    else if ( first == second )
    {
        return 0;
    }
    else
    {
        return 1;
    }
}

int cmp2  (void * a, void * b)
{
    return ( *(int *)a - *(int *)b );
}


void cmp3 (void *a, void *b)
{
    char one = *(char *)a;
    char two = *(char *)b;

    if (one == two){
        printf("The two values are equal");
    }

    else
    {
        printf("The two values are not equal");
    }

}

void QSort(void *v[],int left, int right, int (*compare)(void *first, void *second))
{
    int i, last;
    void swap (void *v[],int ,int);


    if(left >= right){
        return;
    }

    swap(v,left,(left+right)/2);
    last=left;
    for(i=left+1;i<=right; i++){
        if((*compare)(v[i],v[left])<0){
            swap(v,++last,i);
        }
    }

    swap(v,left,last);
    QSort(v,left,last-1,compare);
    QSort(v,last+1,right,compare);
}




int main()
{
    int first = 23;
    int second = 4;
    int third = 5;
    int temp[3];//={22,4,36,64,0};

    temp[0] = (void *)&first;
    temp[1]=(void *)&second;
    temp[2]=(void *)&third;

    QSort(temp, 0, 2, cmp1(.....));

    for(int n=0;n<3;n++){
        printf("%d ",*((int *)temp[n]));
    }
    return 0;
}

Upvotes: 1

Views: 894

Answers (3)

user207064
user207064

Reputation: 665

temp is not an integer array, it should be array of integer pointers.

line 

   int temp[3];

should be replaced with

   int *temp[3];

Upvotes: 0

Lee Duhem
Lee Duhem

Reputation: 15121

QSort(temp, 0, 2, cmp1(.....));

shoud be

QSort(temp, 0, 2, cmp1);

If foo is name of a function, then you use foo() to call it, and use foo to pass it as an argument to another function that requires a function pointer.

Upvotes: 1

Vaughn Cato
Vaughn Cato

Reputation: 64308

cmp1 is really the best way. It should always perform correctly.

cmp2 is close. It would work most of the time, but if you are dealing with very large integers, the results would be wrong.

cmp3 is definitely not right. The values are actually ints, but are being treated as chars. The results would be meaningless.

Upvotes: 2

Related Questions