String sorting alphabetically using array of pointers

Question

I wish to sort the strings alphabetically using swap function. The swap function doesn't seems to work. Should i pass the entire array of strings into swap as well ?

#include <stdio.h>
#include <string.h>
void swap (char *s, char *t);
void main()
{
    char *name[10] = {"Noida","Lucknow","Kanpur","Mohali","Chandigarh","Mumbai","Kerala","Chennai","Bangalore","Indore"};
    char *temp;
    printf("The names are :\n");
    for(int i = 0; i < 10; i++)
    {
        printf("%s\n",name[i]);
    }
    printf("\nSORTING ALPHABETICALLY - \n\n");
    for (int i = 0; i < 10; i++)
    {
        for (int j = i + 1; j < 10; j++)
        {
            if(strcmp(name[i],name[j])>0)
                swap(name[i],name[j]);
        }
    }
    for(int i = 0; i < 10; i++)
    {
        printf("%s\n",name[i]);
    }
}
void swap (char *s, char *t) //Not swapping
{
    char *temp;
              temp = s;
              s = t;
              t = temp;
}

You are swapping the function arguments, not what they point to. These are copies of what you passed, which are then forgotten. — Weather Vane
– Weather Vane, Commented Mar 11, 2019 at 8:09
I suggest the function should take the array (pointer), and the indices of the two elements to be swapped, or, as one answer. — Weather Vane
– Weather Vane, Commented Mar 11, 2019 at 8:14
Instead of writing your own sorting code you should use qsort — 4386427
– 4386427, Commented Mar 11, 2019 at 8:32

Quimby · Accepted Answer · 2019-03-11 08:16:50Z

5

You are passing the pointers by copy. The function operates on its own local variables which are copies of the pointers to those strings, not the pointers to the main variables. So it can change the strings but not those variables(= values of those pointers). This should fix it:

void swap (char **s, char **t) 
{
    char *temp;
    temp = *s;
    *s = *t;
    *t = temp;
}

Edit: As stated in the comment bellow: Then call it like swap(&name[i],&name[j]);

edited Mar 11, 2019 at 8:16

answered Mar 11, 2019 at 8:15

Quimby

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2 Comments

Blaze Over a year ago

And of course changing the function call to swap(&name[i], &name[j]);.

Gamal Othman Over a year ago

@Blaze or just swap( name+i, name+j );

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